bitbake: bitbake: Bootstrap pytest for self-tests

To support running the bitbake self-tests using pytest, add a
pytest.ini This enables these tests to be run using the following
command from the bitbake directory.

  pytest

For now, testpaths only includes the bitbake selftests.

Add a note to the README.

(Bitbake rev: 79bc14003000ab439262272dae6a99961f7c14c7)

Signed-off-by: Peter Hoyes <Peter.Hoyes@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/README

@@ -53,3 +53,8 @@ testsuite as follows:
 
     export PATH=$(pwd)/bin:$PATH
     bin/bitbake-selftest
+
+The testsuite can alternatively be executed using pytest, e.g. obtained from PyPI (in this
+case, the PATH is configured automatically):
+
+    pytest