improve `projects/{project_id}/jobs/{job_id}/testruns` performance (API and UI)

[andrejev]

testruns api returns the test results with stderr and stdout traces in the case of error (which might be upto 100mb). In many case, we don't need these traces. It makes sense to define a new function which returns stderr and stdout for specific test case only and add an additional parameter (e.g traces=False) in the testruns to exclude traces from results. Huge size of testruns result also affects the UI performance.