Makefile: use develop --user based on feature presence

And not based on Python version.  It was observed that platforms based
on Python 2.6, such as EL6, do ship with setuptools that has support
for `--user`.  This eases considerably the development environment
on these platforms.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

Makefile

@@ -12,7 +12,7 @@
 #
 
 PYTHON=$(shell which python)
-PYTHON26=$(shell $(PYTHON) -V 2>&1 | grep 2.6 -q && echo true || echo false)
+PYTHON_DEVELOP_ARGS=$(shell if ($(PYTHON) setup.py develop --help 2>/dev/null | grep -q '\-\-user'); then echo "--user"; else echo ""; fi)
 VERSION=$(shell $(PYTHON) setup.py --version 2>/dev/null)
 DESTDIR=/
 AVOCADO_DIRNAME=$(shell echo $${PWD\#\#*/})
@@ -107,10 +107,10 @@ clean:
 	for MAKEFILE in $(AVOCADO_PLUGINS); do\
 		if test -f $$MAKEFILE/Makefile -o -f $$MAKEFILE/setup.py; then echo ">> UNLINK $$MAKEFILE";\
 			if test -f $$MAKEFILE/Makefile; then AVOCADO_DIRNAME=$(AVOCADO_DIRNAME) make -C $$MAKEFILE unlink &>/dev/null;\
-			elif test -f $$MAKEFILE/setup.py; then cd $$MAKEFILE; $(PYTHON) setup.py develop --uninstall $(shell $(PYTHON26) || echo --user); cd -; fi;\
+			elif test -f $$MAKEFILE/setup.py; then cd $$MAKEFILE; $(PYTHON) setup.py develop --uninstall $(PYTHON_DEVELOP_ARGS); cd -; fi;\
 		else echo ">> SKIP $$MAKEFILE"; fi;\
 	done
-	$(PYTHON) setup.py develop --uninstall $(shell $(PYTHON26) || echo --user)
+	$(PYTHON) setup.py develop --uninstall $(PYTHON_DEVELOP_ARGS)
 	rm -rf avocado_framework.egg-info
 	rm -rf /var/tmp/avocado*
 	rm -rf /tmp/avocado*
@@ -153,11 +153,11 @@ modules_boundaries:
 	selftests/modules_boundaries
 
 develop:
-	$(PYTHON) setup.py develop $(shell $(PYTHON26) || echo --user)
+	$(PYTHON) setup.py develop $(PYTHON_DEVELOP_ARGS)
 	for MAKEFILE in $(AVOCADO_OPTIONAL_PLUGINS); do\
 		if test -f $$MAKEFILE/Makefile -o -f $$MAKEFILE/setup.py; then echo ">> LINK $$MAKEFILE";\
 			if test -f $$MAKEFILE/Makefile; then AVOCADO_DIRNAME=$(AVOCADO_DIRNAME) make -C $$MAKEFILE link &>/dev/null;\
-			elif test -f $$MAKEFILE/setup.py; then cd $$MAKEFILE; $(PYTHON) setup.py develop $(shell $(PYTHON26) || echo --user); cd -; fi;\
+			elif test -f $$MAKEFILE/setup.py; then cd $$MAKEFILE; $(PYTHON) setup.py develop $(PYTHON_DEVELOP_ARGS); cd -; fi;\
 		else echo ">> SKIP $$MAKEFILE"; fi;\
 	done
 
@@ -165,7 +165,7 @@ link: develop
 	for MAKEFILE in $(AVOCADO_EXTERNAL_PLUGINS); do\
 		if test -f $$MAKEFILE/Makefile -o -f $$MAKEFILE/setup.py; then echo ">> LINK $$MAKEFILE";\
 			if test -f $$MAKEFILE/Makefile; then AVOCADO_DIRNAME=$(AVOCADO_DIRNAME) make -C $$MAKEFILE link &>/dev/null;\
-			elif test -f $$MAKEFILE/setup.py; then cd $$MAKEFILE; $(PYTHON) setup.py develop $(shell $(PYTHON26) || echo --user); cd -; fi;\
+			elif test -f $$MAKEFILE/setup.py; then cd $$MAKEFILE; $(PYTHON) setup.py develop $(PYTHON_DEVELOP_ARGS); cd -; fi;\
 		else echo ">> SKIP $$MAKEFILE"; fi;\
 	done
 
@@ -176,7 +176,6 @@ man: man/avocado.1 man/avocado-rest-client.1
 
 variables:
 	@echo "PYTHON: $(PYTHON)"
-	@echo "PYTHON26: $(PYTHON26)"
 	@echo "VERSION: $(VERSION)"
 	@echo "DESTDIR: $(DESTDIR)"
 	@echo "AVOCADO_DIRNAME: $(AVOCADO_DIRNAME)"
@@ -186,6 +185,7 @@ variables:
 	@echo "COMMIT: $(COMMIT)"
 	@echo "SHORT_COMMIT: $(SHORT_COMMIT)"
 	@echo "MOCK_CONFIG: $(MOCK_CONFIG)"
+	@echo "PYTHON_DEVELOP_ARGS: $(PYTHON_DEVELOP_ARGS)"
 
 .PHONY: source install clean check link variables