Merge topic 'ep-svn-user-pass'

7e80415e79 ExternalProject: Reduce number of local variables for svn logic
e16f65be15 ExternalProject: Don't add SVN auth args if not set

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Merge-request: !9678