test: Allow to add additional commands to prepend

We usually run the CI through the python scripts generating buildkite
pipeline steps. To enable to inject custom CPU templates through the
python scripts, adds a new command line argument `--additional-prepend`
that specifies additional commands to prepend to the generated steps.

Signed-off-by: Takahiro Itazuri <[email protected]>

Author: zulinx86

.buildkite/common.py

@@ -176,6 +176,14 @@ def __call__(self, parser, namespace, value, option_string=None):
     default=None,
     type=str,
 )
+COMMON_PARSER.add_argument(
+    "--additional-prepend",
+    help="Commands to be prepended additionally",
+    required=False,
+    nargs="+",
+    default=[],
+    type=str,
+)
 
 
 def random_str(k: int):
@@ -288,6 +296,7 @@ def _adapt_group(self, group):
                     f"chmod -v a+x {self.binary_dir}/**/*",
                 ]
             )
+        prepend.extend(self.args.additional_prepend)
 
         for step in group["steps"]:
             step["command"] = prepend + step["command"]