tests: Improve tickle tests

tests: Improve tickle tests

It is hard to diagnose failures in the NFS tickle test because there's
no way of telling if the test node doesn't have the tickle or if it
didn't get propagated.

Factor out check_tickles() into local.bash and give it some
parameters.

Have the NFS test call it first to ensure the tickle has been
registered.  Then use new function check_tickles_all() to ensure the
tickle has been propagated to all nodes.  Give this a bit of extra
time (double the timeout) just in case we're racing with the update.

Add a useful comment to the CIFS test so that I stop asking myself how
the test could ever have worked reliably.  :-)

Signed-off-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Amitay Isaacs <amitay@gmail.com>
Pair-programmed-with: Amitay Isaacs <amitay@gmail.com>

(Imported from commit bafb9151ccb5722df36f9ba168716f4f4fa01cdc)