#6 Fix Random Call Bug

[kenmaro3]

Improvement of random call

Currently, the random call picks up the one random peer to call,
however, it can pick up the one who already in the call,
if he/she is picked, current call is shut down and new call is forced to start.
Need to fix this.

• Investigate how we can get the list of peers who are already on the call.
• Extract out on-call-list from random-pickup-list