Fix personality fact gathering for 'Virtual Chassis' without 'RE0' member.

Routing engines are numbered after the virtual chassis members.
Hence a routing engine number 0, RE0, does not necessarily exist.
So search facts for the first key matching '^RE\d'.
Merge pull request #117 from stoned/vc-non-re0

Fix personality fact gathering for 'Virtual Chassis' without 'RE0' membe...