ctest_update: Capture svn failures in more places

Issue #16646 (closed) reported a regression caused by a commit that got through our test suite because ctest_update did not capture the failure of svn log. The test passed because svn update still worked and produced the proper output, but it does not verify that authorship information is extracted. Although the latter is not covered explicitly by the test, the operations performed for it were failing unnoticed. Update cmCTestVC and related code paths to support failure of steps other than the update itself. Update cmCTestSVN to capture failure of svn log and a few other operations.