bug 965803 -- add repo init and sync flags

I verified that this does work:
<pre>
$ REPO_INIT_FLAGS='-q --no-repo-verify' ./config.sh emulator-jb
....
+ ./repo init -u git://github.com/mozilla-b2g/b2g-manifest -b master -m emulator-jb.xml -q --no-repo-verify
</pre>