Remove hard requirement on sys-proctable

[aemadrid]

sys/proctable is required to stop nsqadmin but sys/proctable does not run in JRuby and will not for the foreseable future [1]. This commit removes the hard requirement and produces warning while trying to require sys/proctable and raise an exception when trying to stop nsqadmin.

Added a test to make sure the exception is raised and modified other tests (4) that depend on being able to stop nsqadmin so they are skipped if sys/proctable is not available.

[1] djberg96/sys-proctable#18

[bschwartz]

Hi Adrian,

Thanks for the PR! I'm a bit confused about how this will work. Perhaps I'm missing something though.

Won't you also need to modify the nsq-cluster.gemspec to not include sys-proctable as a runtime dependency? And if you do that, then if someone uses nsq-cluster in another project, they will have to explicitly include sys-proctable if they want the ability to stop nsqadmin?

@freerobby You're a JRuby guy, any wise ideas how to solve this? See here for context: wistia/nsq-ruby#11

[freerobby]

@bschwartz @aemadrid I think the best way to solve this problem is either (1) a drop-in replacement for sys-proctable that is MRI and JRuby-compatible, or (2) a code path fork based on Ruby version that uses an alternate JRuby-compatible library if JRuby is detected. I'm going to close this PR since it doesn't bring us closer to either of those options, but if you see a path that I don't, leave a comment and we'll re-examine.

For future PRs, please refrain from reformatting otherwise unmodified code -- it makes the diff harder to read, and also I'd hate to see a bunch of hard work get held up in a stylistic debate.

Thanks you for taking the time to put this together -- I'll definitely keep this feedback/use case in mind next time I'm in there!