Generalize test targets in Makefile

Only a single recipe is defined for running go test or the sharness
tests. The short/expensive/race variants of the tests are defined
using target-specific variable values.

Makefile

@@ -1,11 +1,4 @@
 
-ifeq ($(TEST_NO_FUSE),1)
-go_test=go test -tags nofuse
-else
-go_test=go test
-endif
-
-
 all:
 	# no-op. try:
 	#   make install
@@ -34,27 +27,35 @@ nofuse:
 
 test: test_expensive
 
-test_short: build test_go_short test_sharness_short
+test_short: test_go_short test_sharness_short
 
-test_expensive: build test_go_expensive test_sharness_expensive
+test_expensive: test_go_expensive test_sharness_expensive
 
 test_3node:
 	cd test/3nodetest && make
 
-test_go_short:
-	$(go_test) -test.short ./...
+ifeq ($(TEST_NO_FUSE),1)
+GO_TEST_FLAGS = -tags nofuse
+endif
+
+test_go_short: GO_TEST_FLAGS += -test.short
+test_go_short: test_go
+
+test_go_expensive: test_go
+
+test_go_race: GO_TEST_FLAGS += -race
+test_go_race: test_go
 
-test_go_expensive:
-	$(go_test) ./...
+test_go: build
+	go test $(GO_TEST_FLAGS) ./...
 
-test_go_race:
-	$(go_test) ./... -race
+test_sharness_short: test_sharness
 
-test_sharness_short:
-	cd test/sharness/ && make
+test_sharness_expensive: SHARNESS_MAKE_FLAGS += TEST_EXPENSIVE=1
+test_sharness_expensive: test_sharness
 
-test_sharness_expensive:
-	cd test/sharness/ && TEST_EXPENSIVE=1 make
+test_sharness: build
+	cd test/sharness/ && $(MAKE) $(SHARNESS_MAKE_FLAGS)
 
 test_all_commits:
 	@echo "testing all commits between origin/master..HEAD"