If the etcd member is not found, then it has already been removed, and
kubeadm reset should immediately complete the 'remove-etcd-member'
phase. Previously, the phase would complete only once the
exponential-backoff retry expired, up to 3 minutes duration.
This commit also fixes a semantic error in etcd.GetMemberID. Previously,
the function returned 0 if no member was found, but 0 is not a valid
member ID.