This reverts commit f97f0525, reversing
changes made to 800bcd8e.

LEARNER-76

Introduces a mgmt. command that retrieves course runs from catalog service in order to update marketing urls for the courses found in course metadata cache (i.e. CourseOverview). This also provides an updated utility to retrieve course sharing url.

There are a number of Django Signals that are on the modulestore's
SignalHandler class, such as SignalHandler.course_published. These
signals can trigger very expensive processes to occur, such as course
overview or block structures generation. Most of the time, the test
author doesn't care about these side-effects.

This commit does a few things:

* Converts the signals on SignalHandler to be instances of a new
  SwitchedSignal class, that allows signal sending to be disabled.

* Creates a SignalIsolationMixin helper similar in spirit to the
  CacheIsolationMixin, and adds it to the ModuleStoreIsolationMixin
  (and thus to ModuleStoreTestCase and SharedModuleStoreTestCase).

* Converts our various tests to use this new mechanism. In some cases,
  this means adjusting query counts downwards because they no longer
  have to account for publishing listener actions.

Modulestore generated signals are now muted by default during test runs.
Calls to send() them will result in no-ops. You can choose to enable
specific signals for a given subclass of ModuleStoreTestCase or
SharedModuleStoreTestCase by specifying an ENABLED_SIGNALS class
attribute, like the following example:

    from xmodule.modulestore.tests.django_utils import ModuleStoreTestCase

    class MyPublishTestCase(ModuleStoreTestCase):
        ENABLED_SIGNALS = ['course_published', 'pre_publish']

You should take great care when disabling signals outside of a
ModuleStoreTestCase or SharedModuleStoreTestCase, since they can leak
out into other tests. Be sure to always clean up, and never disable
signals outside of testing. Because signals are essentially process
globals, it can have a lot of unpleasant side-effects if we start
mucking around with them during live requests.

Overall, this change has cut the total test execution time for
edx-platform by a bit over a third, though we still spend a lot in
pre-test setup during our test builds.

[PERF-413]

This reverts commit bde0f7b2, reversing
changes made to 71693c3a.

This reverts commit dec4034b, reversing
changes made to ef55cc4f.

This reverts commit f7a0c1d9, reversing
changes made to dec4034b.

https://openedx.atlassian.net/browse/TNL-5008

MA-2189

This will leverage the nose attrib plugin to allow us
to break tests apart on our build system to run
in parallel on separate nodes.

TNL-2180

MA-1767

Update Zendesk ticket to correctly add group.

Add logic to hide new audit certs