Pabot

- Metadata merging from all runs https://github.com/mkorpela/pabot/pull/412 Thank you DirkRichter !
- Replace the deprecated function getargspec to getfullargspec https://github.com/mkorpela/pabot/pull/406 Thank you hicycle !

Stacktrace listener could cause side-effect failure in specific cases.
This has now been fixed by updating dependency to robotframework-stacktrace 0.4.1

This release drops support to Python 2.7.
And adds [robotframework-stacktrace](https://github.com/MarketSquare/robotframework-stacktrace) when running with normal robot without listeners.

So console output will be like this:

pabot tmp
2021-06-08 21:21:23.083356 [PID:3664] [0] [ID:0] EXECUTING Tmp.Testing
2021-06-08 21:21:23.394708 [PID:3664] [0] [ID:0] Execution failed in Tmp.Testing with 1 failing test(s)
==============================================================================
Tmp
==============================================================================
Tmp.Testing
==============================================================================
Testing
Traceback (most recent call last):
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
File ../testing.robot:2
T: Testing
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
File ../testing.robot:4
Keyer
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
File ../testing.robot:8
Fail foo
______________________________________________________________________________
| FAIL |
foo
------------------------------------------------------------------------------
Tmp.Testing | FAIL |
1 test, 0 passed, 1 failed
==============================================================================
Tmp | FAIL |
1 test, 0 passed, 1 failed
==============================================================================
Output: ../pabot_results/0/output.xml