Convert mdsal-netconf-ssh to OSGi DS

This is a rather simple blueprint, just convert the single component we
have here. Since Declarative Services shutdown dependents before
deactivating the reference, we can also squash the unbind() method.

JIRA: NETCONF-956
Change-Id: If3c5af7bd212583d0f37af085a33468a8d905802
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>