Return a lit.Test.Result object from TestRunner's executeShTest()

Return a lit.Test.Result object from TestRunner's executeShTest()

Summary:
For various clang analyzer tests, which were unsupported, I got lit
exceptions, similar to the following:

    Exception during script execution:
    Traceback (most recent call last):
      File "utils/lit/lit/run.py", line 190, in execute_test
        result = test.config.test_format.execute(test, lit_config)
      File "tools/clang/test/Analysis/analyzer_test.py", line 11, in execute
        if result.code == lit.Test.FAIL:
    AttributeError: 'tuple' object has no attribute 'code'

This is because executeShTest() in utils/lit/lit/TestRunner.py is
supposed to return a lit.Test.Result object, but in case of unsupported
tests, it returns a plain tuple.

Fix this by returning a properly initialized lit.Test.Result object
instead.

Reviewers: rnk, rafael, modocache

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D33579

llvm-svn: 303943