fixed 'check' task config so it can be run inside a subproject folder

otherwise it would fail due to relative file paths like this:

$ cd subprojects/groovy-test
$ gradle check
> Unable to create a Checker: cannot initialize module RegexpHeader - unable to load header file config/checkstyle/codeHeader.txt
removed unused checkstyle config.xml file

- it was replaced by checkstyle.xml
Merge pull request #257 from darxriggs/checkstyle-subprojects-fix

Checkstyle subprojects fix
GROOVY-6366 - Update Jline to 2.11
GROOVY-6367 - Update JANSI to 1.11
define dependency versions as project properties and reuse them in subprojects
GROOVY-3302: Some tests are CPU load dependent

Test still fails from time to time on the CI-Server, so give it even more time
Merge branch 'master' into jdk8