[k6] Report failure rate for all tests in a single plot

Instead of separate plots of test failures for each test case,
we have one single plot showing failures.

Issue-ID: CPS-2347
Signed-off-by: danielhanrahan <daniel.hanrahan@est.tech>
Change-Id: Ie79b75c34903a7df2037474b3536d4867c1a61e0
2 files changed