testing/testcase: use realpath to compare paths

This supports the case where some paths used for shared parts are
symlinks
3 jobs for feat/collect_garbage_collect_faster_query in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:39:10

passed SlapOS.Eggs.UnitTest-Master.Python3

00:44:30

passed SlapOS.Eggs.UnitTest-Master.Python3