Retry if interrupted before mMessageThread has joined

Bug: 24342101

If interrupted during mMessageThread.join(), retry the join instead of
assuming the thread has joined and continuing.  Continuing to destroy
the context will cause a segfault when the message thread attempts to
use the destroyed context.

Change-Id: I3213091a0e996449bceb403dffca3063786d5a65
(cherry picked from commit 2f25ce77)