Adding SNMP4SDN features

1) Feature Tests Pass: https://jenkins.opendaylight.org/snmp4sdn/job/snmp4sdn-merge/128/testReport/
2) Features Comply with Guidelines: https://git.opendaylight.org/gerrit/gitweb?p=snmp4sdn.git;a=blob;f=features/src/main/resources/features.xml;h=59154026adab443d7914d7f30d7bb0183dfca34f;hb=master
	a) Feature Names: odl-snmp4sdn-all, odl-snmp4sdn-snmp4sdn
	b) Features Descriptions: OpenDaylight :: SNMP4SDN :: All, OpenDaylight :: SNMP4SDN :: Plugin
	c) Features Start-Levels: No start-levels on <bundle> elements or <feature> elements
3) Features Tested: Features have been tested for functionality with
	a) feature:install odl-snmp4sdn-snmp4sdn
	b) feature:install odl-snmp4sdn-all
4) Integration Test Impact: No

Signed-off-by: ylhsieh <ylhsieh@itri.org.tw>