Check if a device is added to the cache before returning.

For incoming connections, we don't have the device in the Settings cache.
After we tried to readPairedDevices, check if we added to the cache.
If we successfully added it, continue with the connections, else bail out.

Bug id: 2160617

Change-Id: I25f2afba8ef6d2c32a7940f967cf12f1321ad9e0