Run openapi-generator as "current" user, not root. (apache#13674)

This tool will happily run without the user existing in the passwd
files, and by running as this user we don't have a lot of files owned by
root left hanging around.

Additionally, only reset the _spec_ file, not the entire repo

clients/gen/common.sh

@@ -27,6 +27,7 @@ function gen_client {
     lang=$1
     shift
     docker run --rm \
+        -u "$(id -u):$(id -g)" \
         -v "${SPEC_PATH}:/spec" \
         -v "${OUTPUT_DIR}:/output" \
         openapitools/openapi-generator-cli:v${OPENAPI_GENERATOR_CLI_VER} \

scripts/ci/openapi/client_codegen_diff.sh

@@ -50,7 +50,7 @@ mkdir -p "${GO_CLIENT_PATH}"
 # generate client for target patch
 mkdir -p "${GO_TARGET_CLIENT_PATH}"
 
-git reset --hard "${previous_mainline_commit}"
+git checkout "${previous_mainline_commit}" -- "$SPEC_FILE"
 ./clients/gen/go.sh "${SPEC_FILE}" "${GO_TARGET_CLIENT_PATH}"
 
 diff -u "${GO_TARGET_CLIENT_PATH}" "${GO_CLIENT_PATH}" || true