Wrap whole test with several publish/unpublish in same bulk_op.

Please note that this is a squshed commit and the work of:
Symbolist, macdiesel, nedbat, doctoryes, muzaffaryousaf and muhammad-ammar

Make unpublish raise the same errors in split and old-mongo when asked to unpublish a DIRECT_ONLY_CATEGORY

This is a new TestCase base class, intended for situations where
you only want to initialize course content in the setUpClass(),
as opposed to setUp(). This is done for performance reasons, since
many test cases only use courses in a read-only fashion,
particularly in LMS tests.

This commit also converts the following modules to use this new
base class:

  lms/djangoapps/ccx/tests/test_ccx_modulestore.py (38s -> 4s)
  lms/djangoapps/discussion_api/tests/test_api.py (2m45s -> 51s)
  lms/djangoapps/teams/tests/test_views.py (1m17s -> 33s)

only require ccx-keys once

get_current_ccx will now expect a CourseKey instance as its argument, and will raise a value error if this expectation is not met.

document reason for local import

add special methods to pass attribute setting and deletion through to the wrapped modulestore

add __setattr__ and __delattr__ per code review, update __init__ to work with new methods

style change per code review

clean up context manager usage as recommended by code review

remove unused code and imports

convert modulestore type tests to use the `get_modulestore_type` api, remove unused imports

code quality: add docstrings

increase coverage for utils tests

fix bug found in testing.

increase test coverage on modulestore wrapper

code quality fixes

code-quality: ignore import error, but mark site for future consideration

remove references to middleware that were missed previously

use key apis rather than local implementation of key conversion.  remove local implementationa

remove spurious test for attribute

fix test setUp to avoid unneeded flattening

code quality fixes

add security check ensuring that the coach is coach for *this* CCX.

prevent ccx/deprecated course id problems

1.  do not allow ccx objects to be created if the course id is deprecated
2.  filter out any ccx memberships that involve deprecated course ids (in case there are bad ccxs in the database)

Fix test failures and errors arising from incorrect code path execution

Create context manager to handle unwrapping and restoring ccx values for the modulestore wrapper, employ it throughout modulestore wrapper implementation

Implement the use of CCX opaque keys throughout the ccx code base

include the new custom ccx id package in the github checkouts list

update the coach dashboard wrapper to get CCX information from the incoming course_id, if possible

update function signatures for all view functions to expect CCX as passed by the dashboard wrapper (default to None), remove calls to get_ccx_for_coach as the ccx is passed in.

update reverse calls in python view code to use a CCXLocator for the URL instead of a CourseLocator

use CCXLocator where necessary

use course id to find ccx, instead of thread local

remove unused method and related tests

use course id for getting ccx

provide course id to the get_current_ccx method

ensure the course id passed in is a CourseKey instance of some type whether it starts out as a string or not

use the provided block to figure out what the course_id should be, then get the ccx for that

redirect to ccx dashboard using coach ccx if no ccx is passed in

update student dashboard listing for ccx to build an appropriate url from a CCXLocator, not from the course locator.

refactor building the ccx locator so we don't have to do it repeatedly

begin test refactoring after ccx_keys introduction

Ensure that when access checking happens, the course_locator form of a ccx locator is used.  This ensures that the access check happens against the course and it is not necesarry to duplicate the entire access control structure for the course.

pick up api change in ccx-keys

create and conditionally use a wrapper for the mixed modulestore returned by xmodule.modulestore.django.modulestore

the wrapper will strip and restore ccx values from CourseKey and UsageKey objects

fix return values on a few methods

remove unused symbol

pull updated ccx-keys package

set course_id on the caching descriptor system to avoid api incompatibilities in some subsystems

use ccx.course instead of self.course

fix get method to find course keys from blocks that are not themselves keys but have a location attribute (which will be a key)

if an item coming out of the db has children, restore the ccx to them as well

if the block passed in has a CCX key, unwrap that before we try to look up the override, otherwise it will never be found.

pick up a change in the ccx keys package that allows for stripping CCX identity from a usage key

begin writing tests to cover this modulestore wrapper

remove the switch_pocs view, the url pattern for it, and the tests that covered it

remove the ccx context and the middleware responsible for setting the current CCX.  These are no longer needed

all dashboard views should raise 404 if a ccx is not provided by the coach_dashboard decorator

code quality

prevent errors resulting from trying to `get` a ccx based on non-unique criteria.

remove obsolete usage of ACTIVE_CCX_KEY

fix setUp method for grading tests to properly create grades for the ccx rather than for the course.

clean up reverse calls

code quality

adding docstrings to clarify purpose of this patch

fix bug in getting ccx for coach

fix grading views to properly fetch a ccx-ified course so that grades for that version will be calculated

fix small errors in modulestore implementation

fix errant merge marker

update call to get_current_ccx after key refactoring merged with tab changes