Update mongodb install to support Ubuntu 18.04

[jamessynge]

This is extracted from #578.

[codecov]

Codecov Report

Merging #583 into develop will increase coverage by 0.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           develop    #583      +/-   ##
==========================================
+ Coverage    70.38%   70.5%   +0.12%     
==========================================
  Files           64      64              
  Lines         5520    5520              
  Branches       769     769              
==========================================
+ Hits          3885    3892       +7     
+ Misses        1426    1422       -4     
+ Partials       209     206       -3

Impacted Files	Coverage Δ
pocs/observatory.py	85.75% <0%> (+0.59%)	⬆️
pocs/serial_handlers/protocol_arduinosimulator.py	77.3% <0%> (+1.92%)	⬆️

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[wtgee]

LGTM. I wonder if we should worry about authorization/authentication on the mongodb. If so we might want to set that up here, but could be in a separate PR.

[jamessynge]

Yes, we should definitely worry about it. I just haven't given it enough thought yet.