The `ceph-external-cluster-details-exporter.py` script needs to run under Python2 to support systems that are still running RHEL 7, but it contains Python3 only syntax.  For example, at line 568:

        try:
            output = subprocess.check_output(cmd,
                                             stderr=subprocess.PIPE)
        except subprocess.CalledProcessError as exec:

In Python 2 (2.7.5), `exec` is a reserved word and can't be used like this; the above line results in:

      File "ceph-external-cluster-details-exporter.py", line 578
        except subprocess.CalledProcessError as exec:
                                                   ^
    SyntaxError: invalid syntax