Travis: make stem log a controller trace, and tail stem's tor log

In Travis, make stem log a controller trace to the console.
And tail stem's tor log after failure.

Closes ticket 30591.

.travis.yml

@@ -211,7 +211,7 @@ script:
   ## We run `make check` because that's what https://jenkins.torproject.org does.
   - if [[ "$DISTCHECK" == "" && "$TEST_STEM" == "" ]]; then make check; fi
   ## Diagnostic for bug 29437: kill stem if it hangs for 15 minutes
-  - if [[ "$TEST_STEM" != "" ]]; then make src/app/tor; timelimit -p -t 540 -s USR1 -T 30 -S ABRT python3 "$STEM_SOURCE_DIR"/run_tests.py --tor src/app/tor --integ --log notice --target RUN_ALL; fi
+  - if [[ "$TEST_STEM" != "" ]]; then make src/app/tor; timelimit -p -t 540 -s USR1 -T 30 -S ABRT python3 "$STEM_SOURCE_DIR"/run_tests.py --tor src/app/tor --integ --log TRACE --target RUN_ALL; fi
   - if [[ "$DISTCHECK" != "" && "$TEST_STEM" == "" ]]; then make distcheck DISTCHECK_CONFIGURE_FLAGS="$CONFIGURE_FLAGS"; fi
   ## If this build was one that produced coverage, upload it.
   - if [[ "$COVERAGE_OPTIONS" != "" ]]; then coveralls -b . --exclude src/test --exclude src/trunnel --gcov-options '\-p' || echo "Coverage failed"; fi
@@ -225,7 +225,7 @@ after_failure:
   ## `make distcheck` puts it somewhere different.
   - if [[ "$DISTCHECK" != "" ]]; then make show-distdir-testlog || echo "make failed"; fi
   - if [[ "$DISTCHECK" != "" ]]; then make show-distdir-core || echo "make failed"; fi
-  - if [[ "$TEST_STEM" != "" ]]; then cat "$STEM_SOURCE_DIR"/test/data/tor_log || echo "cat failed"; fi
+  - if [[ "$TEST_STEM" != "" ]]; then tail -1000 "$STEM_SOURCE_DIR"/test/data/tor_log || echo "tail failed"; fi
 
 before_cache:
   ## Delete all gcov files.

changes/ticket30591

+  o Testing (continuous integration):
+    - In Travis, make stem log a controller trace to the console. And tail
+      stem's tor log after failure. Closes ticket 30591.