Add libjpeg-dev to edxlocal play

Because running the tests for thumbnail manipulation requires it
Merge pull request #1655 from edx/edxlocal-libjpeg

Add libjpeg-dev to edxlocal play
defaulting common_hostname to empty string

also extra vars overrides developer sandbox defaults
Merge pull request #1743 from edx/jarv/fix-flag-release

defaulting common_hostname to empty string
Merge pull request #1744 from edx/release

Release
changing null defaults to empty strings to deal with ansible bug
change the repo for certificates and fix checkout
Merge pull request #1745 from edx/jarv/xserver-null-values

changing null defaults to empty strings to deal with ansible bug
Merge pull request #1746 from edx/jarv/fix-cert-checkout

change the repo for certificates and fix checkout
adding helper scripts in /edx/bin

This adds some helper scripts for managing the edx server.