Support dynamic loading of test utils under acts.test_utils.

Bug=26451809

By strategically removing some __init__.py, we enable implicit
namespace packages, which allows modules of the same package to live
in different directories.

Also add a reserved in config files for specifying test util paths.

Usage:
Add "testutils_paths" in config file as a list of strings.
Each string points to a dir where your own test utils are.
Under the dir, the sub-dir structure should follow the same as the
default acts test utils.

e.g.
In config:
"testutils_paths": ["/usr/something/foo"]

On disk:
/usr/something/foo/acts/test_utils/tel/custom_util.py
/usr/something/foo/acts/test_utils/qcom/qxdm_util.py

In code, you can do:
from acts.test_utils.tel import custom_util
from acts.test_utils.qcom import qxdm_util

Change-Id: I920ee66c0f23925f318394e4a0ad341bfa63e114
7 files changed
tree: b08b7d5a264b821cc2a1153d9c8e5951dcae1c25
  1. acts/