test/bluetooth/tester: Re-pair on lost bond

If IUT is acting as a central device and peer lost bond we need
to re-pair to restore bond. PTS is not sending any WID for this
so bonding needs to be initiated implicitly by IUT.

This was affecting GAP/SEC/AUT/BV-25-C qualification test case.

Signed-off-by: Szymon Janc <szymon.janc@codecoup.pl>