check local pip version on --pre flag
support pre_release parameter in virtualenv state
Merge pull request #6592 from mafrosis/pip_amend

Pip amendments
Fix the `test_install_pre_argument_in_resulting_command` test case.

It now checks if the `--pre` output is present in versions >= 1.4 or not in versions < 1.4
Merge pull request #6594 from s0undt3ch/hotfix/6592

Fix the `test_install_pre_argument_in_resulting_command` test case.
Error when persistent mount.unmounted state run does not change mountpoints.

ret['changes']['umount'] is not always defined (only gets set to True when there was a change. never gets set to False).
We need to guard the code against KeyErrors.
Merge pull request #6595 from d--j/patch-1

Error when persistent mount.unmounted state run does not change mountpoints.