scripts: add build-matrix script to ease matching ci

problem: we have good scripts for running in our images locally, but not
always with all the same flags as in CI

solution: add a script, build-matrix, that takes a name from the actions
build matrix and runs docker_run_checks with the same flags as that
matrix entry

scripts/build-matrix

@@ -0,0 +1,64 @@
+#!/usr/bin/env python3
+
+import argparse
+from pprint import pprint
+import json
+import os
+from pathlib import Path
+from re import L
+import platform
+import subprocess as sp
+import shlex
+import sys
+
+p = argparse.ArgumentParser()
+p.add_argument("-p","--platform", default=platform.machine())
+p.add_argument("--interactive", action="store_true")
+p.add_argument("name")
+args = p.parse_args()
+
+my_path = Path(__file__).absolute()
+generate_matrix = my_path.parent.parent.joinpath("src/test/generate-matrix.py")
+docker_run_checks = my_path.parent.parent.joinpath("src/test/docker/docker-run-checks.sh")
+includes = json.loads(sp.check_output([generate_matrix], env={
+    "GITHUB_REF": "refs/heads/master"
+}).decode())["include"]
+matrix = {}
+for b in includes:
+    matrix[b['name']] = b
+
+plt = args.platform
+if plt in ('x86_64', 'amd64'):
+  plt = 'test-install'
+elif plt == 'aarch64':
+  plt = 'arm64'
+suffix = plt
+suffix = f" - {suffix}"
+
+def usage():
+    print("specify the name of a matrix entry as the first argument, from this list:")
+    for tgt in matrix.keys():
+        print(tgt)
+
+tgt = None
+if args.name in matrix:
+    tgt = matrix[args.name]
+else:
+    tgt = matrix.get(f"{args.name}{suffix}", None)
+
+if tgt is None:
+    usage()
+    sys.exit(1)
+
+
+cmd_arr = shlex.split(tgt['command'])
+brk = cmd_arr.index("--")
+if args.interactive:
+    cmd_arr.insert(brk, f"--interactive")
+cmd_arr.insert(brk, "-D")
+cmd_arr.insert(brk+1, f"build/{tgt['image']}")
+print(f"running {cmd_arr} with env={tgt['env']}")
+base_env = dict(os.environ)
+base_env.update(tgt['env'])
+sp.call(cmd_arr, env=base_env)
+