Add a persistent git clone

WARNING: This adds an infinite loop to around git clone
(under git_clone function)
I am adding this because I have lots of problems with my local proxy,
and I got lots of messages like this while trying to provision a
devstack instance.

STDOUT: Cloning into ANYREPO...
STDERR: error: RPC failed; result=22, HTTP code = 408

Which is because of connection latency, but if I try one more time it
will work.

The loop:

        while true; do
            git clone $GIT_REMOTE $GIT_DEST
            [[ $? -eq 0 ]] && break
        done
Probably there is better ways to fix it but this is my quick & dirty
solution for now