Move the test for 'mergeinfo --log' to log_tests.py so we can validate the
output.

log_tests.py already has all the infrastucture to validate log messages,
don't see a ton of value in moving it around or duplciating it.

* subversion/tests/cmdline/mergeinfo_tests.py
  (mergeinfo_log, test_list): Remove mergeinfo_log and move it...

* subversion/tests/cmdline/log_tests.py
  (mergeinfo_log, test_list): here



git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1548251 13f79535-47bb-0310-9956-ffa450edef68