[backend-jvstm-infinispan] Downgrade required infinispan isolation level to READ_COMMITTED

  * The STM handles the required verifications.  We should be able to still
    ensure strict serializability for the programmer.  However, the
    implementation is not yet completed in the InfinispanRepository
[test-backend-jvstm-common] Preloading is no longer required for jvstm-infinispan cache loader

  * After disabling writeSkewCheck in Infinispan transaction system, we are
    able to also disable the cache loader's preload at startup
Merge pull request #122 from smmf/feature/adjust-jvstm-ispn-to-read-committed

Feature/adjust jvstm-ispn to read committed

  * Downgrade required infinispan isolation level to READ_COMMITTED while still enforcing strict serializability for the programmer.