Create option to filter Os by min livepeer version used

[leszko]

Add the ability to specify by Broadcaster the minimum acceptable go-livepeer version from Os. It works in the following manner:

1. Broadcaster specifies a flag -orchMinLivepeerVersion 4.3.1
2. During the discovery/selection process, B excludes all Os with the version below 4.3.1
3. In the case of O/T topology, the version of O is taken into consideration, then while serving a segment, O will reject Ts that didn't upgrade.

[codecov]

Codecov Report

Attention: Patch coverage is 76.74419% with 10 lines in your changes are missing coverage. Please review.

Project coverage is 57.37820%. Comparing base (6e49ae2) to head (f83dce8).

Additional details and impacted files

@@                 Coverage Diff                 @@
##              master       #3050         +/-   ##
===================================================
+ Coverage   57.32866%   57.37820%   +0.04954%     
===================================================
  Files             92          92                 
  Lines          15685       15722         +37     
===================================================
+ Hits            8992        9021         +29     
- Misses          6091        6099          +8     
  Partials         602         602                 

Files	Coverage Δ
cmd/livepeer/livepeer.go	50.33113% <100.00000%> (+0.33113%)	⬆️
core/livepeernode.go	68.18182% <100.00000%> (ø)
core/orchestrator.go	78.31933% <100.00000%> (+0.07312%)	⬆️
server/broadcast.go	80.00000% <100.00000%> (+0.04310%)	⬆️
server/mediaserver.go	67.50484% <100.00000%> (+0.03146%)	⬆️
core/capabilities.go	83.69565% <86.20690%> (+0.16151%)	⬆️
cmd/livepeer/starter/starter.go	7.15005% <0.00000%> (-0.02892%)	⬇️

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Files	Coverage Δ
cmd/livepeer/livepeer.go	50.33113% <100.00000%> (+0.33113%)	⬆️
core/livepeernode.go	68.18182% <100.00000%> (ø)
core/orchestrator.go	78.31933% <100.00000%> (+0.07312%)	⬆️
server/broadcast.go	80.00000% <100.00000%> (+0.04310%)	⬆️
server/mediaserver.go	67.50484% <100.00000%> (+0.03146%)	⬆️
core/capabilities.go	83.69565% <86.20690%> (+0.16151%)	⬆️
cmd/livepeer/starter/starter.go	7.15005% <0.00000%> (-0.02892%)	⬇️