[lit] Don't check output of commands used in `shtest-timeout.py` test.
[lit] Don't check output of commands used in `shtest-timeout.py` test.

If the system is under heavy load 1 second might not be long enough
for it to produce output which could lead to spurious test failures.
What matters is that the right test cases reach a timeout.

rdar://problem/40221572

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@332985 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm