fuzz: accelerate non-crash detection

We spend much time waiting for the timeout program during the minimization
process until it passes a time limit. This patch hacks the CLOSED (indicates
the redirection file closed) notification in QTest's output if it doesn't
crash.

Test with quadrupled trace input at:
  https://bugs.launchpad.net/qemu/+bug/1890333/comments/1

Original version:
  real	1m37.246s
  user	0m13.069s
  sys	0m8.399s

Refined version:
  real	0m45.904s
  user	0m16.874s
  sys	0m10.042s

Note:

Sometimes the mutated or the same trace may trigger a different crash
summary (second-to-last line) but indicates the same bug. For example, Bug
1910826 [1], which will trigger a stack overflow, may output summaries
like:

SUMMARY: AddressSanitizer: stack-overflow
/home/qiuhao/hack/qemu/build/../softmmu/physmem.c:488 in
flatview_do_translate

or

SUMMARY: AddressSanitizer: stack-overflow
(/home/qiuhao/hack/qemu/build/qemu-system-i386+0x27ca049) in __asan_memcpy

Etc.

If we use the whole summary line as the token, we may be prevented from
further minimization. So in this patch, we only use the first three words
which indicate the type of crash:

SUMMARY: AddressSanitizer: stack-overflow

[1] https://bugs.launchpad.net/qemu/+bug/1910826



Signed-off-by: Qiuhao Li <Qiuhao.Li@outlook.com>
Reviewed-by: Alexander Bulekov <alxndr@bu.edu>
Tested-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <SYCPR01MB350251DC04003450348FAF68FCAB0@SYCPR01MB3502.ausprd01.prod.outlook.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>