Drop Pyrun on OS X Installer and replace it with virtualenv.

[djallado]

Branch: master (OS X Installer)

Expected Behavior: Download video or update language pack will continue without error.

Current Behavior: There's an error when downloading videos or updating language pack.
Here's the screenshoot:

Steps to reproduce:

1. Login as Admin User.
2. Click Video tab.
3. Navigate to the topic tree and choose your preferred video to download.
4. Click on Download new selected video button. Then error will occur like in the screenshot:
   

[jamalex]

@benjaoming Is it possible that the cron server isn't getting passed the correct settings, and hence isn't accessing the shared database (the one migrations should already have been run against)?

[djallado]

@aronasorman.

Our plan after dropping pyrun:

1. In our script we will check the minimum python package of 2.7.9+.
2. If below, then we will prompt the user to to upgrade python.
3. We will include kalite source also.
4. Pip packages are included in .dmg.

[benjaoming]

@jamalex could be a settings discrepancy, but only in case the OSX installer does use a custom settings module. As for the latest 0.14.x and develop branches, they are using the fix for the --settings option.

@djallado in case the OSX installer uses one settings module (--settings or DJANGO_SETTINGS_MODULE) for running kalite manage setup, then kalite start has to use the same and vice versa.

[cpauya]

This is a manifestation of the issue on #100 - we can ignore this for now and close this after #100 is closed.

[cpauya]

PyRun will still be used for release 0.16. Moving this to 0.17.

[benjaoming]

Is this going to be using PEX?

[mrpau-richard]

Fixed in 429

[mrpau-richard]

@benjaoming Yeah, We're now using PEX in KA Lite OS X installer closing this issue.