fix broken unclaimed_physical_drives method

The list returned by `phyisical_drives` contains two element lists where
the first element is the OS mount path/name for the device. This then
needs to be turned into the device unique name in order to use the
`disk_owner` method.

This also fixes the unclaimed physical disks validation in the cinder
barclamp.

Fixes bnc#830868
Merge pull request #1027 from mapleoin/unclaimed

fix broken unclaimed_physical_drives method
Remove unneeded code

Initialization of node.crowbar["crowbar"] and
node.crowbar["crowbar"]["network"] is already done in
NodeObject.create_new_role().
The NodeObject.allocated method was removed

Use allocated? instead. This seems to be collateral damage from
commit b12b969f.
Initialize "allocated" attribute when creating the node object

Apart from being somewhat cleaner also avoids breaking the true/false
convention for the NodeObject.allocated? method.
Make allocated? behave according to ruby conventions

'?' methods should only return a boolean