Add LUKS section to FAI disk entry

Descriptive title for this enhancement

Add the LUKS section in FAI plugin

Actual behavior

Actually we can manage normal hard drive, LVM and RAID but we miss the LUKS section

Expected behavior

That we can create and manage LUKS section

Step by step description of new behaviour

1. Click on Add LUKS

2. Fill the next fields like the pictures

In place of sda2,sda3 we need the device path like /dev/sda2

3. Add a solution to add a passphrase

The LUKS section will look closely to the RAID one, it need only that we may use the same partition than LVM or RAID without the condition to have 2 partitions.

It make the next FAI configuration with the a primary partition and raid

disk_config sda fstabkey:device disklabel:msdos bootable:1
primary              /boot              200MB        ext2       rw 
primary              -                  -            -          rw 
primary              -                  -            -          rw 
disk_config cryptsetup fstabkey:device
raid1                -                  sda2,sda3    -          rw 

It must look like this one at the end

disk_config sda fstabkey:device bootable:1
primary              /boot              200MB        ext2       rw
primary              -                  0-           -          -

disk_config cryptsetup
luks:"passphrase"    -                  /dev/sda2    -          -