resulttool/regression: Improve matching of poor ptest test names

Some test case naming is poor and contains random strings, particularly
lttng/babeltrace but also curl. Truncating the test names works since they
contain file and line number identifiers which allows us to match them
without the random components, or in the case or curl, test IDs.

Going forward we may be able to improve the test names but this
tweak allows historical test results to work in reports.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>