Remove old Maven pom variables from rexster cfg

When I copied titan-rexster's XML config file from titan-dist, I
should have fixed or deleted these Maven variable references.  Deleted
for now.
Cleanup and add assertions to TitanRexsterTest

This requries recent Rexster fixes to pass.  The Rexster HEAD commit
must be at least commit 2621f8cc2b4003261f27293a002af65714a25ade.