zdtm: Replace `ps -p` with `kill -0`

The -p argument to `ps` is not supported by Busybox v1.19.4. Sending
signal 0 with the `kill` command is an alternative way to check
whether a process is still running.

http://www.linuxjournal.com/content/monitoring-processes-kill-0

Signed-off-by: Christopher Covington <cov@codeaurora.org>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
zdtm: Make use of $test consistently

The $test variable was being used without being locally defined in
the start_test function. Define it locally for uniformity with other
functions and use it where convenient. Also make the definition in
case_error local for uniformity with other functions.

Signed-off-by: Christopher Covington <cov@codeaurora.org>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
mnt: Don't delay external mount points

It looks like criu constantly postpones external bind mounts. I'm trying to resolve
when we manage to break this (when I did ext-mount-map they for some reason didn't).
Meanwhile, this patch fixes it back.

Reported-by: Saied Kazemi <saied@google.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>