Implement conditional steps execution

[miltolstoy]

Work items:

• [x] initialize conditional steps logic - https://github.com/Samsung/Universum/pull/737

• [x] implement artifacts collection - https://github.com/Samsung/Universum/pull/716

• [x] handle only one branch step set - https://github.com/Samsung/Universum/pull/749

• [x] create basic documentation - https://github.com/Samsung/Universum/pull/748

• [x] implement report artifacts collection - https://github.com/Samsung/Universum/pull/750

• [x] reformat tests - https://github.com/Samsung/Universum/pull/790

• [x] add tests for artifacts preprocessing - https://github.com/Samsung/Universum/pull/791

• [x] implement artifacts & report artifacts preprocessing - https://github.com/Samsung/Universum/pull/794, https://github.com/Samsung/Universum/pull/795

• [x] implement Configuration support instead of Step for branch steps (link) - https://github.com/Samsung/Universum/pull/808, https://github.com/Samsung/Universum/pull/809

• [x] temporarily disable having children for conditional step - https://github.com/Samsung/Universum/pull/812

• [x] allow other configurations to be launched after the conditional step - https://github.com/Samsung/Universum/pull/816

• [x] implement critical flag logic - https://github.com/Samsung/Universum/pull/817

• [x] temporary disable steps addition - https://github.com/Samsung/Universum/pull/819

• [x] merge into master - https://github.com/Samsung/Universum/pull/820

• [x] fix bugs found - https://github.com/Samsung/Universum/pull/825

• [ ] implement steps addition and multiplication

• [ ] design & implement step filtering for conditional steps (link)

• [ ] check work with the if_env_set flag

• [ ] check background execution

• [ ] check work with TeamCity tags (link1, link2)

• [ ] handle config where conditional step has children (link): run child steps before branch steps, use critical flag logic

See discussions and proposals under https://github.com/Samsung/Universum/issues/636

[miltolstoy]

Preliminary development plan was created during the task discussion:

1. Step(..., if_succeeded=..., if_failed=...)
2. ? Step -> If / IfStep / ConditionalStep
3. ? ConditionalStep(...).then(...).else(...)
4. ? conditional_step >> then | else

"?" steps are subject to discussion.

[i-keliukh]

Children

handle config where conditional step has children Note that there are several separate design decisions:

• how to deal with children in conditional step itself
• what to do with children in "true branch" and "false branch"
• do we have to put "true branch" and "false branch" into the same structure as conditional step itself?