Replace regex-based parser in console.listen() with uri.parse()
Fix #447: console.connect() must require uri, not host/port
Remove debug message from console.connect()
Fix #534: Segmentation fault after two bad wal_mode settings

Other changes:

 - "" or NULL=ffi.cast('void *', 0) now resets option to default value
 - app/cfg.test.lua converted to TAP format
fixed misprint, added small cfg{} test
Merge branch 'master' of https://github.com/tarantool/tarantool