ofono: Tighten pkill regexp for killing ofonod daemon at end of test

The regexp is not bound to either end of the process name, so despite
the fact that the test script changed its effective process name to
‘ofonod_’, the regexp ‘ofonod’ still matches that, and hence the script
was killing itself, which was causing the systemd unit it was running as
to fail, and hence the overall test to fail.

Tighten the pkill regexp to match at the end of the process name to
avoid this.

Bug-Apertis: https://bugs.apertis.org/show_bug.cgi?id=681


Signed-off-by: Philip Withnall <philip.withnall@collabora.co.uk>

Differential Revision: https://phabricator.apertis.org/D2284