Avoid use of '/tmp' for pip operations
    
    `ipa-run-tests` is not an entry_point script, so
    pip during an installation of ipatests package checks
    if the file path is executable. If not - just don't set
    the executable permission bits.
    
    pip's working directory defaults to /tmp/xxx.
    Thus, if /tmp is mounted with noexec such scripts lose
    their executable ability after an installation into
    virtualenv. This was found on Travis +
    freeipa/freeipa-test-runner:master-latest docker image.
    
    Build directory of pip could be changed via env variable
    PIP_BUILD, for example.
    
    Fixes: https://pagure.io/freeipa/issue/8009
    Signed-off-by: Stanislav Levin <slev@altlinux.org>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>