Various cleanup to run_command

* Rename fail_on_rc_non_zero to check_rc, much more succinct.
* Simplify method defintion
* Fix command module and drop shell=shell option; whether to use
  shell is determined by if args is a list.

Add run_command to module_common and update modules to use it.

This updates apt, apt_repository, command, cron, easy_install, facter,
fireball, git, group, mount, ohai, pip, service, setup, subversion,
supervisorctl, svr4pkg, user, and yum to take advantage of run_command
in module_common.py.

This adds a helper method that modules can call to execute a command via
subproces.  It takes two arguments: the command to run and
keyword options that control how the process is executed.  Supported
options are: fail_on_rc_non_zero, close_fds, and executable.
fail_on_rc_non_zero will call fail_json if the command fails.  If
args is a list, the command will be run with shell=False; otherwise, if
a string, it will be run with shell=True.  Otherwise, run_command() returns
the returncode, stdout, and stderr.

hacking/env-setup: remove unused sys import.

Prevent permission denied when cloning

Without read permission to the current working directory, git-clone will
fail:
root@host:~$ sudo -u git -H git clone \
  git://github.com/ansible/ansible.git /home/git/ansible
fatal: Could not change back to '/root': Permission denied

This commit ensures that the working directory is changed to the
parent-folder of the destination before doing the clone.

typo in ssh private key name

EC2 module should report back the public_dns_name too

Fixes #1854.

Updates Arch PKGBUILD to include other man pages

Fix distribution detection - return string instead of functions

add with_sequence lookup plugin

Plugin allows you to do easy counts for items.

Fixes #1848.

Man pages for ansible-pull and ansible-docs are now installed properly

Revert the import of C in script

So we cannot get rid of this one now.

For compatibility with older releases as well as avoiding things like
action: raw executable= show status
to communicate with devices that don't have sh.

shlex.split will strip quotes and it might not even be sh at this point.

Clean up imports (taken from PR #1804)

Fixes the case where variable x is '$y' and y is a dict(foo='bar') and
an attempt to access ${x.foo} is made.

Useful for managing not-UNIX things.