restart_required cfg-param is bool and not string

There was a break to the previous version of the configuration
paramenters API when the configurations parameters were moved to
the database. The actual type of the restart_required parameter
should be a JSON boolean value, and not a string to be compatible
with the previous configuration parameters API.

Change-Id: If45944e25a55813ddf8f80010811da04d667ca19
Closes-Bug: #1379665
cluster_config argument missing in prepare()

Due to a bad merge, the prepare() call in postgresql does
not have cluster_config argument. Added that to make sure
postgres is in line with other data stores.

Change-Id: I1c3e5032447124dae47ae23ebf820fdcf8080588
Closes-Bug: #1380745
Merge "restart_required cfg-param is bool and not string" into proposed/juno
Remove runtime dep on python pbr