testing: fix default snapshot path for logrotate files

logrotate stack uses srv/backup/logrotate
4 jobs for fix/ldd-libnsl
Status Job ID Name Coverage
  External
passed SlapOS-Master.UnitTest-Master

running SlapOS-Master.UnitTest-Master

27992:10:56

running SlapOS.Eggs.UnitTest-Master.Python2

27992:11:06

running SlapOS.Eggs.UnitTest-Master.Python3

27992:10:54