tests: Fix creation/deletion of E.Sources in EDS test backend

tests: Fix creation/deletion of E.Sources in EDS test backend

The E.Sources for testing were being created by calling `cp` in the wrapper
script running around the entire test suite. However, each test case was
tearing down the E.Sources by deleting them. This meant that no E.Source
existed for anything except the first test case in a given test suite.

The fix is to move the file copying inside the test suite’s setup method.