Suppress shutdown hook exception

The code that stats an embedded Cassandra daemon for test purposes
also installs a shutdown hook to kill the daemon.  The hook calls a
method which can also be called from a separate stop method by an
ordinary thread outside the JVM shutdown hook sequence.  This method
attempts to uninstall the shutdown hook once it's done (useful on the
stop path).  However, uninstalling a shutdown hook when the JVM is
trying to exit (the hook path) results in an IllegalStateException.
It's scary looking but not harmful.  This commit makes the method
tolerate and log ISE.
Fix convenience getters in FaunusSchemaManager

FSM defines a general getRelation method, plus convenience methods for
specific relation subtypes.  FSM is just a pair of dumb
ConcurrentHashMaps with no awareness of Titan schema.  FSM.getRelation
delegates to a helper class that knows about Titan's ManagementSystem
API when a retrieval on one of the maps misses.  However, the subtype
helper getters did not delegate.  This led to a confusing NPE in
TitanHadoopGraph.readHadoopVertex's call to
vertex.getTypeManager().getPropertyKey(name); the type was defined in
FSM's helper class, but FSM was ignoring it.  I think this was
unintentional, since the contains methods on FSM also consult the
ManagementSystem-aware helper.
Add some debug statements to readHadoopVertex