Add github.com to ssh known_hosts for jenkins
Merge pull request #337 from edx/will/jenkins-github-known-hosts

Add github.com to ssh known_hosts for jenkins
Use the EDXAPP_LANG var which already exists.
Merge pull request #389 from edx/feanil/lang_var

Use the EDXAPP_LANG var which already exists.
updating from master, resolving conflicts