Unfortunately, grep -P is not ubiquitous, so use awk with two regexps to
simulate the negative forward lookup in the grep -P expression.

Using awk doesn't really make it too unreadable, as using boolean operators
such as && and || might actually make it more intuitive than the extended
regexp.

Tested:
- sudo make -C test zdtm_ns
- sudo make -C test zdtm_nons
Signed-off-by: Filipe Brandenburger <filbranden@google.com>
Acked-by: Andrew Vagin <avagin@parallels.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>