Make run directory self-contained

[lukaszachy]

Use case: As a user I want to send my run directory to another person so they can reproduce it Use case: As a user I want to reproduce same run Use case: As a user I want to know here/how I created the run

Currently one needs to be in correct metadata root so they can execute same run correctly. Since data are copied to run directory it might be good to use it from there unless force is used.

E.g. Command tmt run --id existing_id --after discover --force should work regardless current directory (plans, tests are used from existing run) Command tmt run --id existing_id --force however does the discover step, so it respects current directory to detect plans and tests (and fails if it is not possible)