iotests: Hide timestamps for skipped tests

iotests: Hide timestamps for skipped tests

Currently, the "thistime" variable is not reinitialized on every loop
iteration.  This leads to tests that do not yield a run time (because
they failed or were skipped) printing the run time of the previous test
that did.  Fix that by reinitializing "thistime" for every test.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>