Add more debug logging and error wrapping for running processes

[triarius]

A customer is seeing errors trying to start a process on an exotic platform that we currently don't support. They are getting an error from (*Process).Run. Let's add some debug logging and error wrapping to see what's going on.

[triarius]

I guess technically this catches errors that are not os.PathError that also happen to wrap syscall.EIO. I think it's unlikely that io.Copy will create such a thing, but I'm happy to do a more specific unwrap if we think otherwise.

[v1gnesh]

@triarius Hey, I now see this in the log in the Pipelines page on the site.

2023-12-08 14:33:54 UTC	Error running job: error starting pty: unsupported

The build script I'm using is this
Looking at the above error, at the moment, it looks like I need to work out how to properly patch creack/pty for this platform first. Will email or report back here when ready to continue 👍

[triarius]

@v1gnesh pty is optional, we disable it on windows:

agent/clicommand/bootstrap.go

Lines 370 to 374 in e32d495

	// Turn of PTY support if we're on Windows
	runInPty := cfg.PTY
	if runtime.GOOS == "windows" {
	runInPty = false
	}

Starting the agent with no-pty option will disable it. If getting creack/pty to work on z/OS is not a path you want to pursue, we can disable the PTY on z/OS like we do on windows. But that requires knowing what the value of runtime.GOOS is for z/OS, which you're going to have to fill us in on.

[v1gnesh]

Oh that's a nice option.
GOOS=zos and GOARCH=s390x.

Although the upstream Go compiler has these keywords reserved, the OS's bits haven't fully been upstreamed yet.
But when running the code/build on this platform, looking for these values, it'll work.

[v1gnesh]

@triarius I've successfully run the sample pipeline and all green on the BK site ❤️
Thank you! I'll continue investigating pty and try more BK stuff.