automount: rmtree temp directory
    
    ipa-client-automount uses the host keytab to acquire a TGT. The script
    sets up a temporary directory for its ccache. At the end of the script
    it removes the ccache and temp directory again.
    
    In case of a failed kinit, the ccache is not created and the removal of
    the ccache causes an exception. The automount installer now uses
    shutil.rmtree() to remove the temporary directory and all its content.
    
    Fixes: https://pagure.io/freeipa/issue/7862
    Signed-off-by: Christian Heimes <cheimes@redhat.com>