travis: require sudo in an attempt to avoid build timeouts (#9327)

- Many container builds are timing out frequently during Spack tests in
  Travis CI.

- Travis recommends to try `sudo: required` to see whether this is an
  infrastructure issue or something else.

- added `sudo: required` to all Linux builds.

- added --verbose to `spack test` invocation so that we can see more
  easily what tests it's timing out on.

Signed-off-by: Todd Gamblin <tgamblin@llnl.gov>

share/spack/qa/run-unit-tests

@@ -28,4 +28,8 @@ ${coverage_run} bin/spack help -a
 ${coverage_run} bin/spack -p --lines 20 spec mpileaks%gcc ^elfutils@0.170
 
 # Run unit tests with code coverage
-${coverage_run} bin/spack test "$@"
+extra_args=""
+if [[ -n "$@" ]]; then
+    extra_args="-k $@"
+fi
+${coverage_run} bin/spack test --verbose "$extra_args"