Implement pick_usb_mount()

[tgharold]

Need a function to pick which USB drive target to use given the inputs of:

• usb_base
• usb_prefix (array)
• usb_fiilename
• usb_suffix (array)

Search pattern is to look for all combinations of:

(usb_base)/(usb_prefix)(usb_filename)(usb_suffix)

Example:

usb_base = /mnt/offsite
usb_prefix = A B
usb_filename = BACKUP
usb_suffix = 1 2

Search space is thus:

/mnt/offsite/ABACKUP1
/mnt/offsite/ABACKUP2
/mnt/offsite/BBACKUP1
/mnt/offsite/BBACKUP2