conman:  Re-use successful provisioning APs.

When provisioning, if we have already provisionined successfully, try to
re-use that AP before trying others or scanning.

In addition to speeing up reprovisioning, this makes it easier to decide
that we don't have a known path to the ACS, which is useful for
controlling LED state.

Change-Id: I5c56ef6ee75ad4fcb28b7648dd17b10c1cb598d2
3 files changed