OSD devices should be specified by FQDN

In the osd.rb recipe, devices are specified by the following node attribute:

> devices = node['ceph']['osd']['devices']

As long as each node that this recipe runs on has the exact same OSD device, this works correctly. However, in some cases, nodes running the osd recipe may have different specifications for its devices. For instance, one node might have a volume called "/dev/vdb":

```
"osd": {
"devices": [
{
"data": "/dev/vdb",
"journal": "/dev/vdb"
}
]
}
```

While another node has a volume called "/dev/vdc":
```
"osd": {
"devices": [
{
"data": "/dev/vdc",
"journal": "/dev/vdc"
}
]
}
```

Ideally, we should be able to qualify OSD devices by FQDN so that we don't need to update the attribute every time we have an OSD with a differently named/type of device:

```
"": {
"devices": [
{
"data": "/dev/vdc",
"journal": "/dev/vdc"
}
]
}
```