prov/verbs: Validate attribute structures

Verbs provider should check the fabric, domain and endpoint attributes
when supplied through hints and validate them.  While returning fi_info,
the attributes should be set to correct values.

Signed-off-by: Arun C Ilango <arun.ilango@intel.com>
Signed-off-by: Sean Hefty <sean.hefty@intel.com>
Merge pull request #423 from shefty/master

prov/verbs: Validate attribute structures