Git Quarentines git receive hooks, i.e. can't git clone during pre-receive.

Git receive places the receive pack in a quarantined directory.
It's not possible to update any refs in this directory. This breaks build scripts that fetches from other git repos. 

More information about the changes is here:

https://git-scm.com/docs/git-receive-pack#_quarantine_environment
https://github.com/git/git/commit/722ff7f876c8a2ad99c42434f58af098e61b96e8