test: use port 0 instead of common.PORT
Checklist
-
make -j8 test
(UNIX), orvcbuild test nosign
(Windows) passes -
commit message follows commit guidelines
Affected core subsystem(s)
Description of change
Use port 0 instead of common.PORT to follow writing test guideline. This is a part of Code And Learn at NodeFest 2016 Challenge in Tokyo.