osdmaptool/test-map-pgs.t: fix escaping to fix run

Run failed always running into the '|| cat $OUT' case due
to bad escaping of '\t'. This is caused by different shells
on different distros (e.g. bash on SUSE vs dash on Ubuntu).

Use 'grep -P ' and fix the regex to make it shell independet.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
(cherry picked from commit be70c1ffe36cea56e3213bd71a47c27d7fa2a068)