Gracefully handle findDeadLockedThreads() not supported

ThreadMXBean.findDeadLockedThreads() might not be supported by the VM and will
then throw UnsupportedOperationException.  If this is the case then don't init
the cause of the ConditionTimeoutException in ConditionAwaiter.await(), but
still throw it.
Merge pull request #16 from jjst/master

Gracefully handle findDeadLockedThreads() not supported