Use external_volumes resource parameter to map storage items to right home and cache

Define a plugin parameter like


In Ansible a external_volumes variable will be available which is a string. This contains the storage items in the order the user selected it. The external_volumes var will be populated by the SRC system.

To get /home and /dcache-cache mounted from the right storage items we need to map the volume_id to a disk id.
For example first volume_id is ddc30b53-105e-4113-9379-c7d3ec9d90e5 then /dev/sdb1 is the first storage item selected.
```
ls -l /dev/disk/by-id/
lrwxrwxrwx 1 root root 9 Jan 6 15:09 scsi-SQEMU_QEMU_HARDDISK_ddc30b53-105e-4113-9379-c7d3ec9d90e5 -> ../../sdb
lrwxrwxrwx 1 root root 10 Jan 6 15:09 scsi-SQEMU_QEMU_HARDDISK_ddc30b53-105e-4113-9379-c7d3ec9d90e5-part1 -> ../../sdb1
```