scripts/validate: Fix git rev-parse when doing local builds

When doing local builds (i.e. without $DRONE_REPO and $DRONE_PULL_REQUEST,
or $DRONE_COMMIT_REF set), the build fails with "fatal: Needed a single
revision" in `scripts/validate`:

```
> make REPO=tserong
[...]
Running validation
Running: go vet
refs/heads/wip-add-virtualSize
fatal: Needed a single revision
FATA[0032] exit status 128
make: *** [Makefile:11: ci] Error 1
```

If I run the commands in `scripts/validate` by hand, I see this:

```
> git symbolic-ref -q HEAD && REV="origin/HEAD" || REV="HEAD^"
refs/heads/wip-add-virtualSize
> echo $REV
origin/HEAD
> headSHA=$(git rev-parse --short=12 ${REV})
fatal: Needed a single revision
```

I don't know if this is just something weird about my environment, but
if I change "origin/HEAD" to "HEAD", it works fine:

```
> headSHA=$(git rev-parse --short=12 HEAD)
> echo $headSHA
eb27fbf6e678
```

Signed-off-by: Tim Serong <tserong@suse.com>
(cherry picked from commit 9707ff0)

# Conflicts:
#	scripts/validate

scripts/validate

@@ -11,12 +11,31 @@ PACKAGES="$(find . -name '*.go' | grep -Ev '.pb.go' | xargs -I{} dirname {} | \
 echo Packages: ${PACKAGES}
 echo Running: go vet
 go vet ${PACKAGES}
+<<<<<<< HEAD
 echo Running: golint
 for i in ${PACKAGES}; do
     if [ -n "$(golint $i | grep -v 'should have comment.*or be unexported' | grep -v 'just return error instead.' | tee /dev/stderr)" ]; then
         failed=true
     fi
 done
 test -z "$failed"
+=======
+
+if [ ! -z "${DRONE_REPO}" ] && [ ! -z "${DRONE_PULL_REQUEST}" ]; then
+	wget https://github.com/$DRONE_REPO/pull/$DRONE_PULL_REQUEST.patch
+	echo "Running: golangci-lint run --new-from-patch=${DRONE_PULL_REQUEST}.patch"
+	golangci-lint run --new-from-patch="${DRONE_PULL_REQUEST}.patch"
+	rm "${DRONE_PULL_REQUEST}.patch"
+elif [ ! -z "${DRONE_COMMIT_REF}" ]; then
+	echo "Running: golangci-lint run --new-from-rev=${DRONE_COMMIT_REF}"
+	golangci-lint run --new-from-rev=${DRONE_COMMIT_REF}
+else
+	git symbolic-ref -q HEAD && REV="HEAD" || REV="HEAD^"
+	headSHA=$(git rev-parse --short=12 ${REV})
+	echo "Running: golangci-lint run --new-from-rev=${headSHA}"
+	golangci-lint run --new-from-rev=${headSHA}
+fi
+
+>>>>>>> 9707ff03 (scripts/validate: Fix `git rev-parse` when doing local builds)
 echo Running: go fmt
 test -z "$(go fmt ${PACKAGES} | tee /dev/stderr)"