utils/docker-run: add NO_NETWORK variable

It is sometimes useful to be able to do an offline build, to make sure
the build works properly without network access, so this commit adds a
NO_NETWORK environment variable to our docker-run script, which for
example allows to do:

$ ./utils/docker-run make source
$ NO_NETWORK=1 ./utils/docker-run make

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

utils/docker-run

@@ -21,7 +21,7 @@ declare -a docker_opts=(
     --user "$(id -u):$(id -g)"
     --workdir "$(pwd)"
     --security-opt label=disable
-    --network host
+    --network "$([ "${NO_NETWORK:-0}" -eq 1 ] && echo none || echo host)"
 )
 
 declare -a mountpoints=(