fixed check for block device

prepare_luks.sh

@@ -1,12 +1,13 @@
 #!/bin/bash
 
 # Overwrite default variables from config file
+cd /installer
 [ -f ./config.sh ] && source config.sh
 
 
 # Check if partition exists
 disk2=$disk"p3"
-if [ -b $disk2 ]
+if ! [ -b $disk2 ]
 then
   echo $disk2 does not exist!
   exit
@@ -18,4 +19,4 @@ mkdir -p /srv/data
 cryptsetup luksFormat $disk2
 cryptsetup luksOpen $disk2 data
 mkfs.ext4 /dev/mapper/data
-mount /dev/mapper/data /srv/data
+mount /dev/mapper/data /srv/data