Fix PeopleProvider activation

Fix PeopleProvider activation

Detected by CSIT, this was broken during MD-SAL API removal. Rework
instantiation to use constructor injection and proper shutdown.
Fixes the following splat:

java.lang.NullPointerException: null
	at org.opendaylight.controller.clustering.it.provider.PeopleProvider$1.onSuccess(PeopleProvider.java:74) ~[bundleFile:?]
	at org.opendaylight.controller.clustering.it.provider.PeopleProvider$1.onSuccess(PeopleProvider.java:70) ~[bundleFile:?]
	at com.google.common.util.concurrent.Futures$CallbackListener.run(Futures.java:1078) ~[bundleFile:?]
	at com.google.common.util.concurrent.DirectExecutor.execute(DirectExecutor.java:30) ~[bundleFile:?]
	at com.google.common.util.concurrent.AbstractFuture.executeListener(AbstractFuture.java:1164) [bundleFile:?]
	at com.google.common.util.concurrent.AbstractFuture.complete(AbstractFuture.java:958) [bundleFile:?]
	at com.google.common.util.concurrent.AbstractFuture.set(AbstractFuture.java:727) [bundleFile:?]
	at com.google.common.util.concurrent.AbstractTransformFuture$TransformFuture.setResult(AbstractTransformFuture.java:247) [bundleFile:?]
	at com.google.common.util.concurrent.AbstractTransformFuture.run(AbstractTransformFuture.java:163) [bundleFile:?]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
	at java.lang.Thread.run(Thread.java:834) [?:?]

Change-Id: I08273c8112ec4d3592440975b77e4ce3467d78a2
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>