restart CouchbaseMock process for each test case
restart CouchbaseMock process for each test case

While it slows down the whole process, it helps to alleviate pain of
coupling between test cases through the mock's imperfection.

Change-Id: I575ae9dcc112e013048692f97ef2b24b23b61dfb
Reviewed-on: http://review.couchbase.org/c/libcouchbase/+/153039
Reviewed-by: Brett Lawson <c8c4369773d7d7226e031f0c4af62e3f38a08510@gmail.com>
Tested-by: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>

couchbase/libcouchbase,kojiromike/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,kojiromike/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,couchbase/libcouchbase,kojiromike/libcouchbase,couchbase/libcouchbase,kojiromike/libcouchbase