Remove int test build context wrapper methods off GradleDistribution.
Changed PreviousGradleVersionExecuter to ReleasedGradleDistribution.

I.e. don't try and be a distribution and an executer at the same time.
Use BasicGradleDistribution through the testing infrastructure, not GradleDistribution.
Fix for use of GradleExecuter as field type.
Always use the test directory for the temp dir, not the working directory.
Rename “GradleDistribution” to “GradleBuiltDistribution” and “GradleBasicDistribution” to “GradleDistribution”.