utils/getdeveloperlib.py: add runtime test parsing

utils/getdeveloperlib.py: add runtime test parsing

This patch extends the Developer class so that it associates each
developer with the runtime tests (in support/testing) is in
responsible for, according to the DEVELOPERS file.

The implementation relies on the unittest module to list all test
cases and does some manual parsing of these test-case objects to get
the actual list of test-cases per test-suite.

A global variable is used to compute the list of unittest only once.

This feature will allow to use the getdeveloperlib module to find
which developer is responsible for which runtime test, and send e-mail
notifications of runtime tests failures.

Signed-off-by: Victor Huesca <victor.huesca@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>