engine() cannot be called before the local_engine was constructed because it
dereferences the pointer local_engine to create a reference.
Consequently, the following error can be seen while running fileiotest:
./core/reactor.hh:854:13: runtime error: reference binding to null pointer of
type 'struct reactor' ASAN:SIGSEGV
Let's switch the test to use app_template.
Signed-off-by: Raphael S. Carvalho <raphaelsc@cloudius-systems.com>
41846256d8