[tests] Import executeCommand() from lit.

 - This is duplicating a small amount of code, but I don't want to consider
   lit's TestRunner module as part of its public API.


git-svn-id: https://llvm.org/svn/llvm-project/dragonegg/trunk@188001 91177308-0d34-0410-b5e6-96231b3b80d8
[tests] Find local test utilities relative to config files.

 - This eliminates the requirement that PYTHONPATH have been modified to point
   into the test source dir.


git-svn-id: https://llvm.org/svn/llvm-project/dragonegg/trunk@188002 91177308-0d34-0410-b5e6-96231b3b80d8
[tests] Import lit modules properly (via its package).

 - Lit itself ensures that its modules can be found, so this completely
   eliminates the need to modify PYTHONPATH.

 - This also makes it more obvious which parts of lit are being used in the
   custom format definition.


git-svn-id: https://llvm.org/svn/llvm-project/dragonegg/trunk@188003 91177308-0d34-0410-b5e6-96231b3b80d8