Allow overriding repository and branch in validate scripts

When running CI in other repositories (e.g. Docker's downstream
docker/engine repository), or other branches, the validation
scripts were calculating the list of changes based on the wrong
information.

This lead to weird failures in CI in a branch where these values
were not updated ':-) (CI on a pull request failed because it detected
that new tests were added to the deprecated `integration-cli` test-suite,
but the pull request did not actually make changes in that area).

This patch allows overriding the target repository (and branch)
to compare to (without having to edit the scripts).

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Makefile

@@ -11,6 +11,11 @@ DOCKERFILE := $(shell bash -c 'source hack/make/.detect-daemon-osarch && echo $$
 DOCKER_GITCOMMIT := $(shell git rev-parse --short HEAD || echo unsupported)
 export DOCKER_GITCOMMIT
 
+# allow overriding the repository and branch that validation scripts are running
+# against these are used in hack/validate/.validate to check what changed in the PR.
+export VALIDATE_REPO
+export VALIDATE_BRANCH
+
 # env vars passed through directly to Docker's build scripts
 # to allow things like `make KEEPBUNDLE=1 binary` easily
 # `project/PACKAGERS.md` have some limited documentation of some of these
@@ -47,6 +52,8 @@ DOCKER_ENVS := \
 	-e TESTDIRS \
 	-e TESTFLAGS \
 	-e TIMEOUT \
+	-e VALIDATE_REPO \
+	-e VALIDATE_BRANCH \
 	-e HTTP_PROXY \
 	-e HTTPS_PROXY \
 	-e NO_PROXY \

hack/validate/.validate

@@ -6,8 +6,8 @@ if [ -z "$VALIDATE_UPSTREAM" ]; then
 	# this is kind of an expensive check, so let's not do this twice if we
 	# are running more than one validate bundlescript
 
-	VALIDATE_REPO='https://github.com/docker/docker.git'
-	VALIDATE_BRANCH='master'
+	VALIDATE_REPO="${VALIDATE_REPO:-https://github.com/docker/docker.git}"
+	VALIDATE_BRANCH="${VALIDATE_BRANCH:-master}"
 
 	VALIDATE_HEAD="$(git rev-parse --verify HEAD)"