support/testing: create default test case for python packages

support/testing: create default test case for python packages

Test cases for python packages are very similar among each other: run a
simple script in the target that minimally tests the package.
So create a new helper class named TestPythonPackageBase that holds all
the logic to run a script on the target.

TestPythonPackageBase adds in build time one or more sample scripts to
be run on the target. The test case for the python package must
explicitly list them in the "sample_scripts" property. The test case
then automatically logins to the target, checks the scripts are really
in the rootfs (it calls "md5sum" instead of "ls" or "test" in an attempt
to make the logfile more friendly, since someone analysing a failure can
easily check the expected script was executed) and then calls the python
interpreter passing the sample script as parameter.
An optional property "timeout" exists for the case the sample script
needs more time to run than the default timeout from the test infra
(currently 5 seconds).

A simple test case for a package that only supports Python 2 will look
like this:

|from tests.package.test_python import TestPythonPackageBase
|
|
|class TestPythonPy2<Package>(TestPythonPackageBase):
|    __test__ = True
|    config = TestPythonPackageBase.config + \
|        """
|        BR2_PACKAGE_PYTHON=y
|        BR2_PACKAGE_PYTHON_<PACKAGE>=y
|        """
|    sample_scripts = ["tests/package/sample_python_<package>.py"]
|    timeout = 15

Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Asaf Kahlon <asafka7@gmail.com>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>