tests: Rename tests/Makefile to tests/Makefile.include

The file is only included from the top Makefile. Rename it to reflect
this more obviously.

Signed-off-by: Fam Zheng <famz@redhat.com>
Message-Id: <1464747811-26917-1-git-send-email-famz@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Makefile

@@ -162,7 +162,7 @@ dummy := $(call unnest-vars,, \
                 common-obj-m)
 
 ifneq ($(wildcard config-host.mak),)
-include $(SRC_PATH)/tests/Makefile
+include $(SRC_PATH)/tests/Makefile.include
 endif
 
 all: $(DOCS) $(TOOLS) $(HELPERS-y) recurse-all modules