Format only.
Fixes #17: Do not generate cobertura-Report by default as the forked lifecycle may lead to bugs in other plugins.

Remove reporting of cobertura, modify check-site to include the cobertura report.
Switch to verify instead of unneeded install.
Fixes #18: Include definitions for jacoco to allow alternate coverage mechanism.

* Include versioning for jacoco.
* Include invoker test check-site-jacoco which checks that cobertura is not executed
for the jacoco case.
* Modify old invoker check-site to verify that jacoco reporting is *not* executed.