Check for Prometheus running in manager state

[iwex]

No description provided.

[iwex]

Not working 😄

[iwex]

Tried to fix, and now seem like it's working

[salsaly4]

Sorry for previous comment, found that the problem was in prometheus-client exposition implementation.

Is it simpler to check for socket like this:

sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
if sock.bind(('127.0.0.1', port)):
    sock.close()
    start_http_server(port)

[salsaly4]

Or even more simpler:

try:
    start_http_server(port)
except:
    pass

[creamsoup]

the prometheus client should be only running by manager daemon. other commands like view, json etc shoulnd't even start prometheus client. if two manager.py with same config is running, this is legit error. so, skipping exception or port being used is not the best solution. seems global is the better solution but global is bad.
I solved this in #824 (pretty much same idea). please comment in the PR if you don't agree.