WP-1209 add bags into getPolicy(Set)BySubject functions

URL: http://jira.webinos.org/browse/WP-1209

Add bag feature to getPolicyBySubject and getPolicySetBySubject policy API methods.

A policy may contain bags. They are required to write subjects with ORed matches.
A bag is a comma separated list used as a match attribute into a subject-match tag.
For example:
<subject-match attr="subject" match="id1,id2,id3" />

getPolicyBySubject and getPolicySetBySubject methods must be able to select and return this kind of policies.