cluster-create creates a security group per trove instance

[Steve McLellan]

create-cluster results in a security group per instance; it makes more sense to me to have a security group for the cluster; there seems little benefit at the cost of stretching quotas.

If I use the cluster API to create a cluster:
  trove cluster-create mongo-cluster mongodb 2.6 --instance flavor_id=2,volume=1 --instance flavor_id=2,volume=1 --instance flavor_id=2,volume=1

and then list instances:
  trove cluster-instances 953e3c9b-4e3f-4912-8992-23f8d00b5ecf
+--------------------------------------+---------------------+-----------+------+--------+
| ID | Name | Flavor ID | Size | Status |
+--------------------------------------+---------------------+-----------+------+--------+
| 4a4c9e45-d8ec-4fcb-8ea8-cbf22504244b | mongo-cluster-rs1-2 | 2 | 1 | BUILD |
| 57a7b0df-93ea-46a1-afe2-10d368b7b45a | mongo-cluster-rs1-3 | 2 | 1 | BUILD |
| 63bdad38-f056-4875-ae8d-c96fc5eddc08 | mongo-cluster-rs1-1 | 2 | 1 | BUILD |
+--------------------------------------+---------------------+-----------+------+--------+

The nlist neutron sec groups:
  neutron security-group-list

--------------------------------------+-----------------------------------------------+---------------------------------------------------------+
| id | name | description |
+--------------------------------------+-----------------------------------------------+---------------------------------------------------------+
| 077ff9f3-9b23-453a-99e3-c263390f048e | SecGroup_57a7b0df-93ea-46a1-afe2-10d368b7b45a | Security Group for 57a7b0df-93ea-46a1-afe2-10d368b7b45a |
| 3f6b2a3f-7416-4b4b-a50a-e97726e07bb5 | SecGroup_4a4c9e45-d8ec-4fcb-8ea8-cbf22504244b | Security Group for 4a4c9e45-d8ec-4fcb-8ea8-cbf22504244b |
| 7692ca69-4dd4-429d-af6b-6dd0679ed13c | SecGroup_63bdad38-f056-4875-ae8d-c96fc5eddc08 | Security Group for 63bdad38-f056-4875-ae8d-c96fc5eddc08 |
+--------------------------------------+-----------------------------------------------+---------------------------------------------------------+

[Auston McReynolds (amcrn)]

this should be a conf, because there are very valid reasons why you'd want separate security-groups for each instance.