Skip coverage tests if coverage driver doesn't exist
Merge pull request #108 from 99designs/skip-coverage-tests-without-coverage-driver

Paratest Test Suite: Skip tests that require code coverage if no driver exists.
fixes #106
Make SuiteLoaderTest less fragile
Remove overly fragile tests, name fixtures so their purpose is clearer.
Removed a type check only test (that was skipped) and a fragile one
Properly close output buffers to fix #107
Failing tests to prove issue #109
PHPUnit warnings cause paratest runs to fail, fixes #109