Merge remote-tracking branch 'remotes/famz/tags/docker-pull-request' into staging

# gpg: Signature made Mon 04 Jun 2018 08:09:27 BST
# gpg:                using RSA key CA35624C6A9171C6
# gpg: Good signature from "Fam Zheng <famz@redhat.com>"
# Primary key fingerprint: 5003 7CB7 9706 0F76 F021  AD56 CA35 624C 6A91 71C6

* remotes/famz/tags/docker-pull-request:
  docker: Update fedora image to 28
  tests/docker/Makefile.include: handle empty TARGET_LIST

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

rules.mak

@@ -1,4 +1,7 @@
 
+# These are used when we want to do substitutions without confusing Make
+NULL  :=
+SPACE := $(NULL) #
 COMMA := ,
 
 # Don't use implicit rules or variables

tests/docker/Makefile.include

@@ -140,7 +140,7 @@ docker-run: docker-qemu-src
 			$(if $V,,--rm) 					\
 			$(if $(DEBUG),-ti,)				\
 			$(if $(NETWORK),$(if $(subst $(NETWORK),,1),--net=$(NETWORK)),--net=none) \
-			-e TARGET_LIST=$(TARGET_LIST) 			\
+			-e TARGET_LIST=$(subst $(SPACE),$(COMMA),$(TARGET_LIST))	\
 			-e EXTRA_CONFIGURE_OPTS="$(EXTRA_CONFIGURE_OPTS)" \
 			-e V=$V -e J=$J -e DEBUG=$(DEBUG)		\
 			-e SHOW_ENV=$(SHOW_ENV) 			\

tests/docker/dockerfiles/fedora.docker

@@ -1,4 +1,4 @@
-FROM fedora:27
+FROM fedora:28
 ENV PACKAGES \
     ccache gettext git tar PyYAML sparse flex bison python3 bzip2 hostname \
     gcc gcc-c++ llvm clang make perl which bc findutils glib2-devel \