script/cpatch.py: add a --run-before argument to run commands

Add a `--run-before` command line argument to cpatch.py that allows
commands to be executed before doing any other layer generation.
This supports actions like customizing packages installed in the
image. Something that can be handy when developing new features.

Signed-off-by: John Mulligan <[email protected]>

Author: phlogistonjohn

src/script/cpatch.py

@@ -221,6 +221,10 @@ def components_selected(self):
     def cephadm_build_args(self):
         return list(self._cli.cephadm_build_arg or [])
 
+    @property
+    def run_before_commands(self):
+        return list(self._cli.run_before or [])
+
     def build_components(self):
         if self._cli.components:
             return self._cli.components
@@ -315,6 +319,11 @@ def parse(cls):
             action="append",
             help="Pass additional arguments to cephadm build script.",
         )
+        parser.add_argument(
+            "--run-before",
+            action="append",
+            help="Add a RUN command before other actions"
+        )
         # selectors
         component_selections = [
             # aggregated components:
@@ -441,6 +450,8 @@ def add(self, component):
     def build(self):
         """Build the container image."""
         dlines = [f"FROM {self._ctx.base_image}"]
+        for cmd in self._ctx.run_before_commands:
+            dlines.append(f'RUN {cmd}')
         jcount = len(self._jobs)
         for idx, (component, job) in enumerate(self._jobs):
             num = idx + 1