Disable lockutils test_synchronized_externally

We're seeing this test fail very regularly in Jenkins and it's become
a serious distraction for everyone.

Disable the test temporarily and use a bug #1095957 to track that the
test itself needs fixing.

Change-Id: I0645d8f5f740d40f83d82e5ef7a048f33a44ac2b
Merge "Disable lockutils test_synchronized_externally"