Fix incorrect hostname detection on Windows

[mpoc]

In some cases, the PowerShell command that is used to detect the hostname will contain extra output before the hostname, e.g. the Microsoft copyright banner or any output that is printed in the PowerShell profiles. This causes invalid hostnames to be sent to the APM server.

This change ensures that the PowerShell output is limited only to the hostname.

[trentm]

@mpoc Thanks!

In some cases,

Do you happen to know what cases? For example, has the default behaviour of powershell.exe on whether to show a logo changed over time? Or perhaps it depends on some system configuration?

Anyway, these changes look good to me.

(Note to self: https://learn.microsoft.com/en-us/powershell/module/microsoft.powershell.core/about/about_powershell_exe?view=powershell-5.1 for notes on the powershell CLI options.)

[mpoc]

Not sure, I couldn't find a definitive answer.

I just wanted to clarify that I wasn't suggesting the banner shows up inconsistently. What I meant was that log messages in profile scripts will break the hostname detection. Likewise, anything printed before the hostname, like the logo banner, will break it for the same reason.

[trentm]

run docs-build

[trentm]

I just wanted to clarify [...]

Understood. Thanks.

[trentm]

This passes "test-windows" before and after. And our tests do include a test of the "system.detected_hostname":

apm-agent-nodejs/test/agent.test.js

Lines 76 to 81 in a1b1f6f

	const system = Object.assign({}, payload.system);
	t.ok(
	system.detected_hostname.startsWith(os.hostname().toLowerCase()),
	'metadata: system.detected_hostname',
	);
	delete system.detected_hostname;

So I think this is good.

I'll follow up with a PR on our specs for this:
https://github.com/elastic/apm/blob/main/specs/agents/metadata.md#hostname

[trentm]

I'll follow up with a PR on our specs for this:
https://github.com/elastic/apm/blob/main/specs/agents/metadata.md#hostname

elastic/apm#851 for that.