VMware: add support for default pbm policy

This is part of the blueprint vmware-spbm-support.
If there is no defined storage policy in the flavor then the default
storage policy will be used. This patch set adds in the definition of
the default storage policy and validates it existence when the service
starts.

DocImpact
    - pbm_enabled - enables storage policy based placement
    - pbm_default_policy - the default policy that will be used if there
      is none in the flavor
    - pbm_wsdl_location (optional) - PBM service WSDL file location URL.
      e.g. file:///opt/SDK/spbm/wsdl/pbmService.wsdl.

Co-authored-by: Radoslav Gerganov <rgerganov@vmware.com>

Change-Id: I1fc5a99c153d815ea735dccda9d2958dba52ec49
Merge "VMware: add support for default pbm policy"