appliance/init: Display uname -a in debug output.

Useful for debugging kernel / architecture issues.  Note this
has no effect if debugging is disabled.

(cherry picked from commit 6c2fad11ac)
(cherry picked from commit 9fc75d4133)

appliance/init

@@ -103,6 +103,7 @@ for f in /sys/block/vd*/queue/rotational; do echo 1 > $f; done
 
 # These are useful when debugging.
 if grep -sq guestfs_verbose=1 /proc/cmdline; then
+    uname -a
     ls -lR /dev
     cat /proc/mounts
     lvm pvs