Implement `LocalHeadCommandRunner.run()`

[johny-b]

GOAL

1. We have a LocalHeadCommandRunner class with method run
2. This method has the same interface as CommandRunnerInterface.run() (https://github.com/ray-project/ray/blob/master/python/ray/autoscaler/command_runner.py)
3. All run arguments are supported in one of the ways:

• Either they work in the same way as in SSHCommandRunner (https://github.com/ray-project/ray/blob/ab1767a5fa3009e6ef1df91f7ae2eeb9b186b1c1/python/ray/autoscaler/_private/command_runner.py#L159), e.g. environment_variables should work
• Or attempt to set them to a non-default value raises a readable exception, e.g. shutdown_after_run should always be false

4. We have a reasonable set of tests

HOW TO START

1. Branch: https://github.com/golemfactory/golem-ray/tree/local-command-runner
2. Install ray and pytest
3. python -m pytest. Two tests fail here - this is where we start.

HOW TO PROGRESS

TDD makes sense here. So:

while not_ready:
     find_single_missing_thing
     add_failing_tests_for_this_thing
     implement_this_missing_thing
     (optional) refactor

[mateuszsrebrny]

cleaning issues (issue no longer needed)