Enable the PBM WSDL to be updated

Enables the PBM WSDL to be updated after a session is created.

An update of the WSDL will set the pbm value to None. This is lazy loaded
so the next access to it will result in the correct session being created.

Change-Id: Id70a7928ca84846018ee0a62ac020ecbeac1f5d6
Merge "Enable the PBM WSDL to be updated"