Trim the test runner log to show only pytest failures/errors

If we get to the `run-tests` phase, we no longer care about messages
from previous steps so we can truncate the log output to only show
pytest failures/errors, reducing log size.

As a fallback, the previous behaviour to print last 5000 log lines was
kept in the case the CI tests fail during setup.

Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>
Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>

.travis.yml

@@ -11,6 +11,7 @@ env:
           TEST_RUNNER_CONFIG=".test_runner_config.yaml"
           PEP8_ERROR_LOG="pep8_errors.log"
           CI_RESULTS_LOG="ci_results_${TRAVIS_BRANCH}.log"
+          CI_BACKLOG_SIZE=5000
     matrix:
         - TASK_TO_RUN="lint"
         - TASK_TO_RUN="run-tests"
@@ -32,5 +33,5 @@ install:
 script:
     - travis_wait 50 ./.travis_run_task.sh
 after_failure:
-    - echo "Test runner output:"; tail -n 5000 $CI_RESULTS_LOG
+    - echo "Test runner output:"; tail -n $CI_BACKLOG_SIZE $CI_RESULTS_LOG
     - echo "PEP-8 errors:"; cat $PEP8_ERROR_LOG

.travis_run_task.sh

@@ -8,6 +8,17 @@ PYTHON="/usr/bin/python${TRAVIS_PYTHON_VERSION}"
 test_set=""
 developer_mode_opt="--developer-mode"
 
+function truncate_log_to_test_failures() {
+    # chop off everything in the CI_RESULTS_LOG preceding pytest error output
+    # if there are pytest errors in the log
+    error_fail_regexp='\(=== ERRORS ===\)\|\(=== FAILURES ===\)'
+
+    if grep -e "$error_fail_regexp" $CI_RESULTS_LOG > /dev/null
+    then
+        sed -i "/$error_fail_regexp/,\$!d" $CI_RESULTS_LOG
+    fi
+}
+
 if [[ "$TASK_TO_RUN" == "lint" ]]
 then
     if [[ "$TRAVIS_EVENT_TYPE" == "pull_request" ]]
@@ -35,3 +46,8 @@ ipa-docker-test-runner -l $CI_RESULTS_LOG \
     --container-image $TEST_RUNNER_IMAGE \
     --git-repo $TRAVIS_BUILD_DIR \
     $TASK_TO_RUN $test_set
+
+if $?
+then
+    truncate_log_to_test_failures
+fi