NO-JIRA: Use DEFAULT_TIMEOUT consistently. Handly for running valgrind tests.

Running tests under valgrind generally causes a timeout because valgrind is
slow.  Some tests were not using the DEFAULT_TIMEOUT. Now all tests are using
that timeout so setting the environment variable QPID_SYSTEM_TEST_TIMEOUT=30 say
will allow tests to run with valgrind.

git-svn-id: https://svn.apache.org/repos/asf/qpid/dispatch/trunk@1633813 13f79535-47bb-0310-9956-ffa450edef68
DISPATCH-72: Sporadic core dumps in dispatch tests.

Added missing lock scopes around calls to python code, this resoloved the
sporadic core dumps (over 1000 test runs overnight with no failures)

Initially I speculated that the problem was that we don't lock the GIL as recommended by
the python C API docs https://docs.python.org/2/c-api/init.html#non-python-created-threads.
Instead we use a separate mutex in the C code.

I attempted to use the GIL but that caused deadlocks. They appeared to be
associated with locking a python mutex in the management agent - this causes
python to unlock and relock the GIL. That allows other threads into the python
code which somehow causes deadlock - I am not sure exactly why.

I believe it is OK to use the separate C mutex *provided* we never create
threads in python code.  If we do that then I think we will need to re-visit the
GIL and figure out how to lock it correctly.

git-svn-id: https://svn.apache.org/repos/asf/qpid/dispatch/trunk@1633814 13f79535-47bb-0310-9956-ffa450edef68