Makefile: Call setup.py develop in "make link"

The "make link" target purpose is to help avocado developers to prepare
environment to run avocado from sources including all subprojects.
Nowadays it requires to run "setup.py develop" manually, but let's
assume wast majority of users of "make link" feature use "setup.py
develop --user" and call it automatically for each subproject (if they
support that).

This way simple "make link" prepares the environment to run avocado from
sources. It can also be used when new targets (plugins) are added
without the need to think which subproject needs to be updated.

NOTE: The subprojects are responsible to add the "python setup.py
develop --user" into the "link" and "unlink" targets.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

Makefile

@@ -27,7 +27,8 @@ all:
 	@echo
 	@echo "Development related targets:"
 	@echo "check:  Runs tree static check, unittests and functional tests"
-	@echo "clean:  Get rid of scratch and byte files"
+	@echo "link:   Runs 'python setup.py --develop' in all subprojects and links the needed resources"
+	@echo "clean:  Get rid of scratch, byte files and removes the links to other subprojects"
 	@echo
 	@echo "Package requirements related targets"
 	@echo "requirements:            Install runtime requirements"
@@ -111,6 +112,7 @@ clean:
 	for MAKEFILE in $(AVOCADO_PLUGINS);\
 		do AVOCADO_DIRNAME=$(AVOCADO_DIRNAME) make -C $$MAKEFILE unlink &>/dev/null && echo ">> UNLINK $$MAKEFILE" || echo ">> SKIP $$MAKEFILE";\
 	done
+	$(PYTHON) setup.py develop --uninstall --user
 
 requirements:
 	- if $$(python -V 2>&1 | grep 2.6 -q); then grep -v '^#' requirements-python26.txt | xargs -n 1 pip install --upgrade; fi
@@ -132,6 +134,7 @@ modules_boundaries:
 	selftests/modules_boundaries
 
 link:
+	$(PYTHON) setup.py develop --user
 	for MAKEFILE in $(AVOCADO_PLUGINS);\
 		do AVOCADO_DIRNAME=$(AVOCADO_DIRNAME) make -C $$MAKEFILE link &>/dev/null && echo ">> LINK $$MAKEFILE" || echo ">> SKIP $$MAKEFILE";\
 	done