build: Add common CLEANFILES and DISTCLEANFILES to common-rules.mk.

By adding common CLEANFILES and DISTCLEANFILES variables to
common-rules.mk, we can remove these from most other Makefiles, and
also clean files more consistently.

Note that bin_PROGRAMS are already cleaned by 'make clean', so I
removed cases where these were unnecessarily added to CLEANFILES.

python/examples/Makefile.am

@@ -23,11 +23,9 @@ EXTRA_DIST = \
 	inspect_vm.py \
 	guestfs-python.pod
 
-CLEANFILES = \
+CLEANFILES += \
 	*.pyc \
-	*.pyo \
-	guestfs-python.3 \
-	stamp-guestfs-python.pod
+	*.pyo
 
 man_MANS = guestfs-python.3
 noinst_DATA = $(top_builddir)/website/guestfs-python.3.html