update test and build workflows to ubuntu 20.04

[hjpotter92]

What does this pull request do? Explain your changes. (required)
Updates test and build workflows to use ubuntu 20.04

Specific updates (required)

• bumped ubuntu version to 20.04
• used Dockerfile to update installation steps
• removed folders not needed to create space on runner

How did you test each of these updates (required)
this PR workflow runs

Does this pull request close any open issues?
old PR this one is based off on: #2841

Checklist:

• Read the contribution guide
• make runs successfully
• All tests in ./test.sh pass
• README and other documentation updated
• Pending changelog updated

[pwilczynskiclearcode]

Would it make sense to merge it with Setup ubuntu container step?

[hjpotter92]

the 'setup ubuntu container' was (and probably is) a temporary step i had to add since github had removed support for ubuntu-18 runners. i do not think we need that step, but just keeping it for future when ubuntu 20 support might go away and we might need to readd the

    container:
      image: ubuntu:18.04

directive for ubuntu-20 :|

[codecov]

Codecov Report

Merging #2846 (36f5e35) into master (a231510) will not change coverage.
Report is 1 commits behind head on master.
The diff coverage is 4.00000%.

@@              Coverage Diff              @@
##              master       #2846   +/-   ##
=============================================
  Coverage   56.70668%   56.70668%           
=============================================
  Files             88          88           
  Lines          19160       19160           
=============================================
  Hits           10865       10865           
  Misses          7699        7699           
  Partials         596         596           

Files Changed	Coverage Δ
cmd/livepeer/livepeer.go	47.61905% <0.00000%> (ø)
cmd/livepeer/starter/starter.go	4.26288% <0.00000%> (ø)
cmd/livepeer_cli/wizard_bond.go	0.00000% <0.00000%> (ø)
cmd/livepeer_cli/wizard_rounds.go	0.00000% <0.00000%> (ø)
cmd/livepeer_cli/wizard_stats.go	0.00000% <0.00000%> (ø)
verification/verify.go	89.16667% <100.00000%> (ø)

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Files Changed	Coverage Δ
cmd/livepeer/livepeer.go	47.61905% <0.00000%> (ø)
cmd/livepeer/starter/starter.go	4.26288% <0.00000%> (ø)
cmd/livepeer_cli/wizard_bond.go	0.00000% <0.00000%> (ø)
cmd/livepeer_cli/wizard_rounds.go	0.00000% <0.00000%> (ø)
cmd/livepeer_cli/wizard_stats.go	0.00000% <0.00000%> (ø)
verification/verify.go	89.16667% <100.00000%> (ø)

[thomshutt]

Massively in favour of this! Looks like the build is failing at the moment though

[pwilczynskiclearcode]

can be merged with setup ubuntu container?

[leszko]

Added one comment. It's fine with me, but please with merging to resolve all discussions and comments from @pwilczynskiclearcode

[leszko]

Do we still use tensorflow? Don't want to get rid of it everywhere?

[thomshutt]

Yeah, if we can tear it out without breaking builds then let's do it. I started trying in #2836 but haven't had time to finish it

[hjpotter92]

oh! that requires quite a lot of changes in go code... which i'd rather not touch in this small-ish PR. would rather bump 2836 with changes from this PR and keep tensorflow removal over in that alone.