convert the conf value into correct type

If options are set in paste file e.g. api-paste.ini for nova, all
the option values passed into AuthProtocol.conf are string type.
So, we should convert the conf value into correct type.

Change-Id: I0367cd6b54ee49f5db6541840539e7700f241f87
Closes-Bug: #1353315
Merge "convert the conf value into correct type"