NO-JIRA: Clean up test_store.cpp async functionality.

Clean up test_store.cpp to allow control over async completion of messsages.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1619814 13f79535-47bb-0310-9956-ffa450edef68
QPID-5855: JAVA Client Can not recieve message with qpid ha cluster "Session exception occured while trying to commit"

The problem: the java client sets the sync flag on tx.commit and then waits for
completion of the entire transaction. According to the 0-10 spec, this is
correct, the commit (or rollback) will not complete until all of the
transactional commands have completed. However the C++ broker was sometimes
completing a commit *before* one of the the corresponding enqueues. It issued
the completions up to the commit (because the commit is makred sync) but there
is a "hole" for the incomplete enqueue. The enqueue is not marked sync so when
this hole is filled no completion is sent and the client hangs.

Fix: make tx.commit a "sync point", that is it behaves like execution.sync and
is not completed till all preceeding commands are complete. Note tx.rollback
does not need modification as it is never completed asynchronously.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1619816 13f79535-47bb-0310-9956-ffa450edef68