[lit] Set parallel mode for coverage tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174017 91177308-0d34-0410-b5e6-96231b3b80d8
[lit] Run the ShUtil tests as part of the test suite.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174018 91177308-0d34-0410-b5e6-96231b3b80d8
[lit] Move unittest adaptor code into discovery module.
 - Also, add a test for it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174019 91177308-0d34-0410-b5e6-96231b3b80d8