Adding vpnservice features

Adding vpnservice features

1) Feature Tests Pass:
https://jenkins.opendaylight.org/releng/job/vpnservice-merge-master/org.opendaylight.vpnservice$vpnservice-features/5/testReport/
2) Features Comply with Guidelines:
https://git.opendaylight.org/gerrit/gitweb?p=vpnservice.git;a=blob;f=features/src/main/features/features.xml;hb=HEAD
        a) Feature Names (prefixed with 'odl-'): odl-vpnservice-core
        b) Features Descriptions: Present
        c) Features Start-Levels: None
3) Features Tested: Features have been tested for functionality with
        a) feature:install odl-vpnservice-core
        b) feature:install odl-vpnservice-core,odl-integration-compatible-with-all
4) Integration Test Impact: None

Change-Id: I77d9187e7f5139dabbec698e7b92bcabfd84ecd6
Signed-off-by: Vishal Thapar <vishal.thapar@ericsson.com>