AAA-169: Advertise PaxWebServer as an OSGi service

AAA-169: Advertise PaxWebServer as an OSGi service

The Pax Web WebContainer implementation registers a ServiceFactory and
uses the class loader of the bundle that obtains the OSGi service
reference. When PaxWebServer is advertised as a service, it causes a
ClassNotFoundEx when initializing shiro b/c it uses the TCCL that is
set by Pax Web obtained from the PaxWebServer's bundle. To alleviate this,
we can advertise a WebServer ServiceFactory so it use the caller's
bundle to get the WebContainer service.

Change-Id: I591c340ccb0551a8138d07ec79443bc648218baf
Signed-off-by: Tom Pantelis <tompantelis@gmail.com>