A fix and a test case for
https://bugs.launchpad.net/tarantool/+bug/750658

--background neither closes nor redirects stdin/stdout/stderr

--background option didn't work properly, since stdin/stdout/
stderr streams were left open and pointing to a terminal.

This lead to a hang when tarantool was started from a
shell script or over ssh.

If --background option is given, we need to fork,
try to create a pid file, close stdin/stdout/stderr
and then initialize the logging
subsystem.