Fix disk matching issue in fuel-agent

Disk matching to be failed if devices have the same 'by-path' links.
With this change disk matching will work fine even on VirtualBox
environment (the latter known as having that issue with links).

Implements: blueprint image-based-provisioning
Change-Id: I511c9756f54acee7d600c3f96372830f8803cbfb
Merge "Fix disk matching issue in fuel-agent"