Makefile.include: pass IOTLAB_NODE to docker

By default if IoT-LAB Cli Tools V3 is used then BINFILE is used to
flash on IoT-LAB. But BINFILE is not built by default when RIOT_CI_BUILD
is set as a ci optimization.

But since before IOTLAB_NODE was not passed to docker when building it
did not know that it should BUILD BINFILE as well, which led to failures
if doing:

$ IOTLAB_NODE=iotlab-m3.grenoble.iot-lab.info BOARD=iotlab-m3 \
  RIOT_CI_BUILD=1 BUILD_IN_DOCKER=1 make -C examples/hello-world/ flash

But if IOTLAB_NODE is passed at is checks for IoT-LAB cli Tools also
happen in the docker container which leads to a make error since those
are not present in docker.

Therefore add BINFILE to BUILD_FILES if RIOT_CI_BUILD is set, but unset
IOTLAB_NODE once INSIDE_DOCKER.

.github/workflows/test-on-iotlab.yml

@@ -70,10 +70,6 @@ jobs:
     env:
       IOTLAB_NODE: auto
       BUILD_IN_DOCKER: 1
-      # Force .bin files generation because these files are used to flash on IoT-LAB and
-      # because compile_and_test_for_board forces RIOT_CI_BUILD which skip .bin
-      # files generation
-      DOCKER_ENVIRONMENT_CMDLINE: -e BUILD_FILES=\$$\(BINFILE\)
       COMPILE_AND_TEST_FOR_BOARD: ./dist/tools/compile_and_test_for_board/compile_and_test_for_board.py
       COMPILE_AND_TEST_ARGS: --with-test-only --jobs=2 --report-xml
       # Exclude applications that are expected to fail or cannot run on iotlab

Makefile.include

@@ -386,6 +386,17 @@ ifneq (,$(IOTLAB_NODE))
   PROGRAMMER ?= iotlab
   # iotlab uses ELFFILE by default for flashing boards.
   FLASHFILE ?= $(ELFFILE)
+  # RIOT_CI_BUILD disables the build of BINFILE which is required for flashing
+  # on IoT-LAB
+  ifeq (1,$(RIOT_CI_BUILD))
+    BUILD_FILES += $(BINFILE)
+  endif
+  # Disable IOTLAB_NODE if inside Docker to avoid including the
+  # iotlab.single.inc.mk file which is useless there: it's only useful for
+  # flashing and this is done outside of Docker.
+  ifeq (1,$(INSIDE_DOCKER))
+    IOTLAB_NODE :=
+  endif
 endif
 
 # Add standard include directories

makefiles/docker.inc.mk

@@ -47,6 +47,7 @@ export DOCKER_ENV_VARS += \
   ELFFILE \
   HEXFILE \
   FLASHFILE \
+  IOTLAB_NODE \
   LINK \
   LINKFLAGPREFIX \
   LINKFLAGS \