build: Remove appliance in 'make clean'

These rules were removed for some reason when I split guestfs-tools
from the libguestfs sources.  However that meant that after 'make
clean' you'd still have the cached appliance and other files under
tmp/.  Re-add the rules.

Author: rwmjones

Makefile.am

@@ -149,6 +149,11 @@ CLEANFILES += \
 	pod2htm?.tmp
 
 clean-local:
+	-rm -rf tmp/libguestfs??????
+	-rm -rf tmp/guestfs.*
+	-rm -rf tmp/.guestfs-*
+	-rm -rf tmp/null.*
+	-find tmp -type s -delete
 	-find . -name '*~' -delete
 
 # Tests.