Force only procs that are participating in the ne Comm to decide what
CID is appropriate. This will have 2 advantages:
* Speedup Comm creation for small communicators: non-participating procs
will not interfere
* Reduce CID fragmentation: non-overlaping groups will be allowed to use
same CID.
Signed-off-by: Artem Polyakov <artpol84@gmail.com>