Description of problem: When heketi is run with devices which are already part of a cluster, a new cluster still gets created. 


Version-Release number of selected component (if applicable): 
Heketi 1.0.0

Heketi is installed from an upstream build as listed here: https://github.com/heketi/heketi/wiki/Installation 

How reproducible: Always


Steps to Reproduce:
1. Run heketi server
2. Run heketi client to add a node and device[1]:  ./heketi-cli load -json=config.json
3. The first run will add the node and device and create a cluster
4. Run it again

Actual results:

A new cluster is created even when creation of physical volume has failed as the device is already part of a cluster.

# ./heketi-cli cluster list
Clusters:
58ccca8f5741edd7f0fd2319b6fa1c86
7492058868e171af4d94334177ad7eb2

# ./heketi-cli load -json=jsons/one_node_one_device.json
Creating cluster ... ID: e71b984c08c994d445ee6c2400097f88
        Creating node rhshdp03.lab.eng.blr.redhat.com ... ID: 9b76b114a87a1b23950d8ae04bcebd11
                Adding device /dev/vdb ... 

# ./heketi-cli cluster list
Clusters:
58ccca8f5741edd7f0fd2319b6fa1c86
7492058868e171af4d94334177ad7eb2
e71b984c08c994d445ee6c2400097f88

Server log:

[sshexec] ERROR 2015/10/15 15:27:18 /home/lpabon/git/go/src/github.com/heketi/heketi/utils/ssh/ssh.go:155: Failed to run command [sudo pvcreate --dataalignment 256K /dev/vdb] on rhshdp03.lab.eng.blr.redhat.com:22: Err[Process exited with: 5. Reason was:  ()]: Stdout []: Stderr [  Can't initialize physical volume "/dev/vdb" of volume group "vg_4bb72f669e4f5106515098dc01e17db4" without -ff


Expected results:

Cluster creation should fail. 

Additional info:


[1] Config file:

{
    "clusters": [
        {
            "nodes": [
                {
                    "node": {
                        "hostnames": {
                            "manage": [
                                "rhshdp03.lab.eng.blr.redhat.com"
                            ],
                            "storage": [
                                "rhshdp03.lab.eng.blr.redhat.com"
                            ]
                        },
                        "zone": 0
                    },
                    "devices": [
                        "/dev/vdb"
                    ]
                }
            ]
        }
    ]
}