requester: Check duplicate key when call registerRequest

Add checking the existing of key {eid, instanceId, type, command}
when call registerRequest.

Tested:
1. Stress polling PLDM sensors.
2. Call pldmtool command to get sensor quickly.
3. Check message "The eid:InstanceID <eid>:<InstanceID> is using."

Change-Id: Ib547eb56e738a7aebfe87ce4967ebf1694e5b3ee
Signed-off-by: Thu Nguyen <thu@os.amperecomputing.com>