(QE-245)  Execution results should be available inside a block

Moving accessors out of test_case and into the dsl so that beaker-rspec
will be able to access them
spec tests for stdout/stderr/exit_code values after calling on
spec test fixes for testing yielding in #on
Merge pull request #22 from anodelman/yield-result

(QE-245)  Execution results should be available inside a block