Introduce a makefile lint rule

This runs pylint over all the python files. Yes, it takes a long while,
but it's the only way to properly analyze the source codes as only in
this way pylint can see all uses of the various modules/classes/etc.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Olivier Tharan <olive@google.com>

Makefile.am

@@ -473,6 +473,10 @@ ganeti:
 check-local:
 	$(CHECK_PYTHON_CODE) $(check_python_code)
 
+.PHONY: lint
+lint: ganeti
+	pylint ganeti $(dist_sbin_SCRIPTS) $(dist_tools_SCRIPTS)
+
 # a dist hook rule for catching revision control directories
 distcheck-hook:
 	if find $(top_distdir) -name .svn -or -name .git | grep .; then \