rpmbuild: fix tests for EPEL6 an 7
    
    The number of `rmtree` calls required for removing a nested directory
    differs between Fedora/python3 and EPEL/python2. It is either bug
    in `mock` module (which is used only for python2) or the `rmtree`
    implementation changed from having recursive calls to having a loop.
    
    I am modifying the test to work on both Fedora and EPEL chroots and
    also adding a special case for EPEL to check that those multiple
    `rmtree` calls affect only the one desired directory.
    
    Relates: #1262