This commit fixes an issue in the VF2Layout and VF2PostLayout pass where
the passes would potentially error in cases when a target was specified
and there were instructions present without any error rates defined. In
such cases the instructions should be treated as ideal (having no error)
and the passes shouldn't fail. In cases where there are no error rates
in the target for VF2Layout the first perfect match should be used, and
for VF2PostLayout it should effectively be a no-op and not select a new
layout.

Fixes Qiskit#8970