ISPN-3245 ReplSyncDistributedExecutorTest.testTaskCancellation fails intermittently

Replace the static counter with a non-static CyclicBarrier in
DistributedExecutorTest. Removes the need for overriding the method in
ReplSyncDistributedExecutorTest.
Clean up commits 5d54f84cbb4d8fb799fb40e3f8fc1ee94c72b1d6 31ef50c9a2fdb628b36ace602a6c879f29b258e7 and 4d4f2e9a2ca1cf657f1fd96163531ae3dbbd142c
ISPN-2753 Drop the dependency on jboss-staxmapper and introduce annotations to declare supported namespaces
ISPN-2753 Drop Staxmapper dependency from LevelDB cachestore
ISPN-3263 Add a 5.3 parser and XSD to the LevelDB cachestore
ISPN-3197 Message ordering of Get and Invalidation can cause L1 to be inconsistent.

* Implemented single entry point for concurrent gets.
* Also support concurrent invalidation for reads with limited blocking
* Added tests for various concurrency/edge issues