Fixes get configuration defaults

Querying for the default configuration of an instance fails when
the my.cnf has keys with no values. ie 'skip-external-locking'.
To fix this, we modify the config template to include values

Change-Id: Iab96ec8cd3f8d79fe2b3946c4e9db094a3acbe93
Closes-Bug: 1285428
Merge "Fixes get configuration defaults"