Closes-Bug: #1390827

spawn storage monitors on selected storage nodes
Issues:
1. As the storage node increases monitor data
   communication increases.
2. In libvirt, buffer size of boot command arguments are
   limited. As the mon increases, there will be increase
   in buffer space and that can cause config overflow issue.

Fix:
1. Added "storage_compute_mon_list" option in testbed.py to
   specify monitors that needs to spawned on selected
   storage compute nodes.
2. Maximum storage monitors set to 10.
3. If this "storage_compute_mon_list" option is not specified
   then storage monitors will be spawned on openstack nodes
   and remaining will be spawned on the storage-compute role
   configured nodes.

Tests:
1. verified setup_storage with "storage_compute_mon_list"
   option enabled/disabled
2. verified add_storage_node with "storage_compute_mon_list"
   option enabled/disabled

Change-Id: Ia5161c9a0c0a0974f94d85277def0831ac615f5d
Merge "Closes-Bug: #1390827" into R1.10