Split matrix server selection into utility function

[andrevmatos]

Follow-up of #3393 , implement some leftovers from that PR

[palango]

I also don't see the send_global function. Did you forget to push that?

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@1d90895). Click here to learn what that means.
The diff coverage is 81.81%.

@@            Coverage Diff            @@
##             master    #3427   +/-   ##
=========================================
  Coverage          ?   76.05%           
=========================================
  Files             ?      100           
  Lines             ?    12960           
  Branches          ?     1824           
=========================================
  Hits              ?     9857           
  Misses            ?     2461           
  Partials          ?      642

Impacted Files	Coverage Δ
raiden/network/transport/matrix/__init__.py	100% <ø> (ø)
raiden/network/transport/matrix/transport.py	75.2% <66.66%> (ø)
raiden/network/transport/matrix/utils.py	75.83% <87.5%> (ø)

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[andrevmatos]

@palango the PR was still in WIP state, I would still add it. But as this was already getting a little big, decided to split the PR and do this only as the promised follow-up of #3393 . The send_global/MS PR will follow shortly

[rakanalh]

Looks good

[ulope]

Lgtm.

One question, below

[ulope]

Shouldn’t this be part of the utility?

[andrevmatos]

@ulope this had too much to do with internals and variables of config, and I wanted to make the utility function as agnostic in relation to config as possible, that's why I kept this outside of it, but can be as easily used outside raiden as any other utility function, so we can say it's already split