AllJOYN-2172 Increased wait time for testJoinSession unit test

On some systems the wait time of 4 seconds was causing the test to fail.
Since there is nothing saying the test must complete in 4 seconds the wait
time has been increased from 4 seconds to 5 seconds to prevent false unit
test failures.

Change-Id: Id3a1109a986208118d4674be209120208e980a50