Receptorctl assert invalid work cmd

[thenets]

(it's only the last commit. The other files are from other PR #445)

Test for:

• The work cancel command does not return a proper status code. #441

Depends on:

• Receptorctl tests refactor #445

cc: @AlanCoding

[thenets]

@shanemcd problem solved, I believe

[thenets]

Test created. Currently failing, cause the work cancel command do not return a non-zero exit code when fail.

[thenets]

@shanemcd @fosterseth this PR will never be auto-merged.
The test is failing because the code is wrong. We need to have a flow to merge and fix broken tests.

[thenets]

I need to finish this issue first:

• Add plugin pytest-github to the receptorctl test suite #495

Then I'll be able to rebase and merge without having the fix.