Fix a small inconsistency when building for CI

We need to clean before attempting to wildcard ebin/test.
To do that, we need to invoke "make clean" separately.

plugins/ci.mk

@@ -27,11 +27,12 @@ ci_verbose = $(ci_verbose_$(V))
 
 define ci_target
 ci-$(1): $(CI_INSTALL_DIR)/$(1)
+	$(verbose) $(MAKE) --no-print-directory clean;
 	$(ci_verbose) \
 		PATH="$(CI_INSTALL_DIR)/$(1)/bin:$(PATH)" \
 		CI_OTP_RELEASE="$(1)" \
 		CT_OPTS="-label $(1)" \
-		$(MAKE) clean ci-setup tests
+		$(MAKE) ci-setup tests
 endef
 
 $(foreach otp,$(CI_OTP),$(eval $(call ci_target,$(otp))))