HHH-9258 OsgiSessionFactoryService does not handle ServiceContributors

Delegate service loading under OSGi to the appropriate OSGi utilities.
Test is currently disabled as it needs some Arquillian love: the fix is verified by the Hibernate Search testsuite.

 - https://hibernate.atlassian.net/browse/HHH-9258

Meant to be integrated in 4.3 and master.

@brmeyer , @sebersole , should I push it?