adds seconds to the file system name

Use the strtime format to get a human-readable timestap as opposed to
time.time()
removes the check for existing filesystems

Since the PID file is used to ensure that only one run of the ZFS test
is occurring at a time, we no longer need to check that the zfs
filesystem is uniquely named.
adds a catch for the KeyboardInterrupt

There will be times when this script will be ended early, however there
could still be some useful results gotten from these short runs, and the
PID file still needs to be cleaned up. So catch the KeyboardInterrupt,
and move onto the rest of the script.
clean up comment