Update edx_provision to fix sandbox envs.
Merge pull request #637 from edx/feanil/default_sites_bug

Update edx_provision to fix sandbox envs.
Make yaml load correctly and reference globals correctly.
Merge pull request #638 from edx/feanil/abbey_yaml_load

Make yaml load correctly and reference globals correctly.
Merge remote-tracking branch 'origin' into jarv/dump_vars