CTestTestMemcheck: Tolerate trailing newlines and tabs from valgrind

When tests

 CTestTestMemcheckDummyPurify
 CTestTestMemcheckDummyValgrind
 CTestTestMemcheckDummyValgrindPrePost
 CTestTestMemcheckDummyValgrindIgnoreMemcheck

run inside a "ctest -T Memcheck" the parent valgrind may add extra
newlines and tabs to the end of the output.  Tolerate this without
failing.
Merge topic 'cleanup-CTestTestMemcheck' into next

67e4571 CTestTestMemcheck: Tolerate trailing newlines and tabs from valgrind