testing: Fix tests passing when test commands fail (#1733)

PR #1563 accidentally changed tests to accept failing commands by
default. (This seems to have been a mistake -- a temporary change
added when debugging that LG neglected to remove before submitting
the PR.)

This can cause tests to pass even though the program crashed, when
a previous run created the correct output file.

---------

Signed-off-by: Brecht Van Lommel <brecht@blender.org>

src/build-scripts/nosanitize.txt

@@ -0,0 +1,3 @@
+# Small leaks that make CI fail, suppress until cause is identified.
+leak:__cxa_thread_atexit
+leak:std::string::_Rep::_S_create

src/testrender/testrender.cpp

@@ -368,7 +368,7 @@ main(int argc, const char* argv[])
 
     // We're done with the shading system now, destroy it
     rend->clear();
-    delete shadingsys;
     delete rend;
+    delete shadingsys;
     return EXIT_SUCCESS;
 }

testsuite/runtest.py

@@ -80,7 +80,7 @@ def make_relpath (path, start=os.curdir):
 outputs = [ "out.txt" ]    # default
 
 # Control image differencing
-failureok = 1
+failureok = 0
 failthresh = 0.004
 hardfail = 0.01
 failpercent = 0.02