java/openjfx8-devel fix build with Gradle 3.2.1

Add a missing build dependency on junit to the Makefile, and fix the
path to Hamcrest in build.gradle. Also, reset MAINTAINER by request of
the current maintainer.

PR: 215677
Reviewed by: brd, Tobias Kortkamp
Approved by: brd (ports)
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D9005