Pass JAVA_OPTS through to signal-cli in json-rpc mode

[kleptog]

Fixes #473

[bbernhard]

Thanks for the PR - very much appreciated!

Just a small thing: Would it be possible to use >> instead of >, so that the changes are appended to the file instead of the whole file getting replaced? Right now, it doesn't matter much, as we do not have anything in there, except your JAVA_OPTS. But maybe at a later point someone writes something to the file as well. And then your > would overwrite those changes again.

What do you think? :)

[kleptog]

Fair enough. When writing it I was going either way, but I don't mind.

Update pushed

[bbernhard]

Many thanks for the contribution!