gsi_util: adding cmd_utils

Adding a run_command function to execute a host command.
Also support reading the stdout and/or stderr of the result if desired,
which might be useful for further parsing and flow decision.

A typical usage will be passing a command sequence:
  cmd_utils.run_command(['echo', '123'])

It also supports running a 'shell' command, by passing a single string:
  cmd_utils.run_command('echo 123', shell=True)

To get the stdout and/or stderr data, just add 'read_stdout=True' and/or
'read_stderr=True':
  cmd_utils.run_command('echo 123', shell=True,
                        read_stdout=True, read_stderr=True),

which returns a namedtuple:
  ('CommandResult', 'returncode stdoutdata, stderrdata').

Note that other keyword arguments will be passed to subprocess.Popen().
e.g., the following command will change current directory to
'my_working_dir' prior to execute the command:
  cmd_utils.run_command('echo 123', shell=True, cwd=my_working_dir)

More usage examples can be found in cmd_utils_unittest.py.

Also adds a run_test.py to search then run ./*tests/*_unittest.py files.

Bug: 70477387
Test: make gsi_util
Test: ./run_test.py
Change-Id: Id3aae935f941818fe7415798937fd07dbbe6ba33

gsi/gsi_util/run_test.py

@@ -0,0 +1,45 @@
+#!/usr/bin/env python
+#
+# Copyright 2017 - The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Script to run */tests/*_unittest.py files."""
+
+from multiprocessing import Process
+import os
+import runpy
+
+
+def get_unittest_files():
+  matches = []
+  for dirpath, _, filenames in os.walk('.'):
+    if os.path.basename(dirpath) == 'tests':
+      matches.extend(os.path.join(dirpath, f)
+                     for f in filenames if f.endswith('_unittest.py'))
+  return matches
+
+
+def run_test(unittest_file):
+  runpy.run_path(unittest_file, run_name='__main__')
+
+
+if __name__ == '__main__':
+  for path in get_unittest_files():
+    # Forks a process to run the unittest.
+    # Otherwise, it only runs one unittest.
+    p = Process(target=run_test, args=(path,))
+    p.start()
+    p.join()
+    if p.exitcode != 0:
+      break  # stops on any failure unittest