t: Fix sporadic test failure in ui/13-admin.t

[okurz]

There was a sporadic failure originally observed in CI runs with very low
failure ratio looking like this

t/ui/13-admin.t .. 14/?
        #   Failed test 'exactly one key present'
        #   at t/ui/13-admin.t line 681.
        #          got: '0'
        #     expected: '1'

I reproduced the problem locally with

runs=200 OPENQA_TEST_TIMEOUT_DISABLE=1 count-fail-ratio make test KEEP_DB=1
TESTS=t/ui/13-admin.t

with results fails: 4. Fail ratio 2.00±1.94%, mean runtime: 39.0±3.0 s.

With make coverage the results were fails 7. Fail ratio 3.50±2.54%,
mean runtime: 80 s so slightly higher fail ratio with double runtime.

This commit uses "wait_for_element" combining the submit action with the lookup
of the resulting table rows to properly synchronize the action and waiting for
result. This fixes the problem. Verified with 400 runs with a computed failure
probability of less than .75%.

Previously I tried to just wait for "#api-keys-tbody > tr" in
"wait_for_element" but running into sporadic issues with similar failure rate
as in before. Apparently the key creation never yields a valid table
representation in this case without retriggering the action.

Related progress issue: https://progress.opensuse.org/issues/158422

[okurz]

Updated

• wait_for_element … or return instead of redundant array size checks
• Using #api-keys-tbody tr:nth-child(2) to select the actual needed second element

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.39%. Comparing base (edc562a) to head (c45f64d).
Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5568   +/-   ##
=======================================
  Coverage   98.39%   98.39%           
=======================================
  Files         392      392           
  Lines       38232    38233    +1     
=======================================
+ Hits        37619    37620    +1     
  Misses        613      613           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.