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>

tests/qemu-iotests/check

@@ -773,6 +773,7 @@ do
     printdiff=false # show diff to reference output?
     status=""       # test result summary
     results=""      # test result details
+    thistime=""     # time the test took
 
     if [ -n "$TESTS_REMAINING_LOG" ] ; then
         sed -e "s/$seq//" -e 's/  / /' -e 's/^ *//' $TESTS_REMAINING_LOG > $TESTS_REMAINING_LOG.tmp