Handle SIGTERM when running commands

[mfischer-zd]

Make Consul treat SIGTERM like it does SIGINT when running commands.
This is especially important when running Consul as a daemon, since
Unix process managers send SIGTERM to restart or terminate a process.

This change is untested on Windows.

Fixes #797

[ryanbreen]

Cool! Does this need testing on Windows? I didn't think they had SIGTERM over there.

[mfischer-zd]

Yes, please. I'm hoping that the new line is a harmless no-op on that platform, but I can't say as I don't run Windows.

[ryanbreen]

Ahh, ok, the question is more "does Windows explode as a result of this patch?" than "is SIGTERM handled properly on Windows?" IIRC, the latter would be impossible to test since Windows doesn't have SIGTERM, but someone with more Windows experience would know for sure.

[highlyunavailable]

It builds on Windows, at least. Usually there's just build failures if something isn't implemented.

I'm running the tests now.

[highlyunavailable]

Also FYI Notify is a variadic function, so signal.Notify(signalCh, os.Interrupt, syscall.SIGTERM) should be valid (see example).

[mfischer-zd]

Mmm, good point @highlyunavailable. If the tests pass, I'll compact the code and update the PR.

[highlyunavailable]

From the look of things this won't break on Windows, there just is no instance in which there will be the syscall.SIGTERM event.

The tests failed all sorts of ways but it doesn't look like anything you did. Mostly Raft couldn't start: agent_test.go:72: err: Failed to start Consul server: Failed to start Raft: There is not enough space on the disk. (20 GB free, though, so maybe this is something to do with memory mapped files)

[mfischer-zd]

Those tests are failing on the master branch too, so let's see what happens when those are fixed.

[mfischer-zd]

Updated commit to use an additional argument to signal.Notify() instead of making another call to it.

[ryanuber]

Thanks, @mfischer-zd. We do already have some handling for SIGTERM here. The behavior of SIGTERM is configurable. If what you're after is a graceful leave, you can set the leave_on_terminate config option, which should cause Consul to invoke the same code path as SIGINT.

[mfischer-zd]

@ryanuber, this patch corrects behavior of consul lock and other tools - it's not related to the behavior of Consul in agent mode. See #797 for further discussion.

[ryanuber]

@mfischer-zd ah that makes sense then, merging this in. The test failures are definitely unrelated to this change. I'll address those separately.