Ignore ClusterLockServiceImplDbBackedTest.

Adds `@Ignore` annotations to both of the tests in `ClusterLockServiceImplDbBackedTest`.

See related [uportal-user@ thread](http://jasig.275507.n4.nabble.com/Does-JpaClusterLockDaoTest-intermittently-fail-for-anyone-else-td4662141.html).

These tests use `Thread.sleep(1500);`.  Sleeping is non-deterministic.  `testDbOnlyTryLockFunction()` false-failed (at least, I hope it's a false failure!) a dev tier build today in the my.wisc.edu project.  This change should prevent that false fail from biting again.

Besides, zapping these tests should save 3 seconds on the `mvn test` run. :)