testsuite: verify core_backtrace in ccpp test

Requires new enough will-crash:
https://github.com/sorki/will-crash/pull/3

Vaguely related to #1051569.

Signed-off-by: Martin Milata <mmilata@redhat.com>
Merge pull request #788 from abrt/extend_core_backtrace_runtest

testsuite: verify core_backtrace in ccpp test