Harmonize headers between both dg-extract-results scripts

    The header of the python version looked like:
    Target is ...
    Host   is ...
    The header of the bash version looked like:
    Test run by ... on ...
    Target is ...

    After this change both headers look like:
    Test run by ... on ...
    Target is ...
    Host   is ...

    The order of the tests is not the same but since dg-cmp-results.sh it
    does not matter much.

contrib/ChangeLog:

	* dg-extract-results.py: Print the "Test run" line.
	* dg-extract-results.sh: Print the "Host" line.