Use a unique index for the running jobs in case of duplicated names

Summary:
The core's PR10374 allows to run the same test several times with a
single call to test_runner.py, by duplicating the test name in the
arguments list. The test_runner.py code has diverged from core, and some
changes will prevent from running duplicated tests.

The test_runner.py script maintains a set of running jobs, indexed by
their test name. This diffs changes the set to a list, and uses a tuple
(test number, test name) as the key. This also requires to pass the
number to the TestResult class in order to rebuild the key when the
job needs to be removed from the list.

Test Plan:

test_runner.py

Reviewers: #bitcoin_abc, deadalnix, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D3367