Move a few test helper functions to a library to avoid having to import
tests from other tests.

* cmdline/relocate_tests.py
  Import from deeptrees instead of switch_tests.
  
* cmdline/svntest/deeptrees.py
  (get_routine_status_state,
   get_routine_disk_state,
   do_routine_switching,
   commit_routine_switching): Move functions here...

* cmdline/switch_tests.py
  (get_routine_status_state,
   get_routine_disk_state,
   do_routine_switching,
   commit_routine_switching): that used to be here here.
   
  Update imports.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1549823 13f79535-47bb-0310-9956-ffa450edef68