BUG-628 Allow configuration to override module based capabilities from remote netconf...

Suitable for devices that do not provide module based capabilities in hello message (most likely do not support ietf-netconf-monitoring).
User can place yang files into cache/schema folder and set the capabilities for these modules into config attribute for netconf-connector.

Change-Id: I541ef08bb5c0328e293f9c732353282ffaf0474d
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>