[PM-1903] Pegasus ensemble manager port is out of range on big systems

[mayani]

When the pegasus-em server starts it tries to use a port based on the user id on the system. If there are many users that port is out of range so the service starts on random free port (I assume).

When we try to interact with the service via the cli (e.g, pegasus-em create runs) it tries to hit the port number that was constructed based on the user id and it fails.

Relevant code line: https://github.com/pegasus-isi/pegasus/blob/master/packages/pegasus-python/src/Pegasus/service/ensembles/commands.py#L18

Example error:
Traceback (most recent call last):
File "/usr/lib64/pegasus/externals/python/requests/models.py", line 380, in prepare_url
scheme, auth, host, port, path, query, fragment = parse_url(url)
File "/usr/lib64/pegasus/externals/python/urllib3/util/url.py", line 392, in parse_url
return six.raise_from(LocationParseError(source_url), None)
File "", line 3, in raise_from
urllib3.exceptions.LocationParseError: Failed to parse: http://127.0.0.1:108751/ensembles

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/lib64/python3.6/site-packages/Pegasus/cli/pegasus-em.py", line 6, in
main()
File "/usr/lib64/python3.6/site-packages/Pegasus/service/ensembles/commands.py", line 699, in main
EnsembleCommand().main()
File "/usr/lib64/python3.6/site-packages/Pegasus/command.py", line 113, in main
cmd.main(args)
File "/usr/lib64/python3.6/site-packages/Pegasus/command.py", line 28, in main
self.run()
File "/usr/lib64/python3.6/site-packages/Pegasus/service/ensembles/commands.py", line 186, in run
response = self.post("/ensembles", data=request)
File "/usr/lib64/python3.6/site-packages/Pegasus/service/ensembles/commands.py", line 54, in post
return self._request("post", path, **kwargs)
File "/usr/lib64/python3.6/site-packages/Pegasus/service/ensembles/commands.py", line 37, in _request
response = requests.request(method, url, **defaults)
File "/usr/lib64/pegasus/externals/python/requests/api.py", line 61, in request
return session.request(method=method, url=url, **kwargs)
File "/usr/lib64/pegasus/externals/python/requests/sessions.py", line 516, in request
prep = self.prepare_request(req)
File "/usr/lib64/pegasus/externals/python/requests/sessions.py", line 459, in prepare_request
hooks=merge_hooks(request.hooks, self.hooks),
File "/usr/lib64/pegasus/externals/python/requests/models.py", line 314, in prepare
self.prepare_url(url, params)
File "/usr/lib64/pegasus/externals/python/requests/models.py", line 382, in prepare_url
raise InvalidURL(*e.args)
requests.exceptions.InvalidURL: Failed to parse: http://127.0.0.1:108751/ensembles

Reporter: @papajim
Watchers:
@papajim
@vahi