Support Armbian by modifying armbianEnv.txt

On Armbian, the kernel commandline (or at least the root device to use)
is stored in armbianEnv.txt rather than cmdline.txt, so update that if
it exists and cmdline.txt does not.

The actual operation on this file is just replacing UUIDs inside the
file, so it works even though the syntax of the file is different.

rpi-clone

@@ -1791,6 +1791,10 @@ qecho ""
 fstab=${clone}/etc/fstab
 cmdline_txt=/boot/cmdline.txt
 cmdline_boot=/boot/cmdline.boot
+if [ ! -f "${clone}${cmdline_txt}" ]; then
+	cmdline_txt=/boot/armbianEnv.txt
+	cmdline_boot=/boot/armbianEnv.boot
+fi
 
 if [ -f "${clone}${cmdline_txt}" ]
 then