[TASK] Run phpLint and phpUnit in different travis builds

phpLint checks php files for compilation errors in travis before
the unit tests are executed. This takes quite some time.
The patch configures travis to run phpLint and phpUnit in different
builds to speed up the process. Additionally, phpLint environment
does not clone phpunit and the introduction package and does no
database initialization.

Change-Id: Ie25ade5b6a8fcf4c4dc0752fc8662c433ea3c33c
Resolves: #50492
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/22624
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Susanne Moog
Tested-by: Susanne Moog
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn