add drcov test

From zhao...@google.com on July 23, 2014 22:24:47

Due to lack of test for drcov2lcov, we have seen regression ( issue #1480 (closed) ), so we should add a few test case for drcov and drcov2lcov.

Original issue: http://code.google.com/p/dynamorio/issues/detail?id=1483