Fix getLibpodTmpDir() on Windows

[sebsoto]

Changes the function to return an absolute path. Without this, EngineConfig.Validate() will return an error on Windows when using the default values.

[openshift-ci]

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[sebsoto]

Before and after:

[Luap99]

Are you trying to port buildah on windows? It would be news to me that buildah can be used on windows.
cc @nalind

[Luap99]

Practically speaking this is a totally useless path on windows. If this should actually work on windows should this not return an actual standard windows temp dir path instead?

[sebsoto]

Are you trying to port buildah on windows? It would be news to me that buildah can be used on windows.

@Luap99 I have an issue open for that: containers/buildah#4010

This change is just fixing something in a shared library, that is obviously broken, and should probably done regardless of the buildah Windows issue.

Practically speaking this is a totally useless path on windows. If this should actually work on windows should this not return an actual standard windows temp dir path instead?

I don't know the full context as to why this path is being used, but the Linux function returns the same path.

common/pkg/config/default_linux.go

Lines 24 to 26 in 6e82793

	func getLibpodTmpDir() string {
	return "/run/libpod"
	}

There is also this other function which actually returns a temporary directory.

common/pkg/config/default_windows.go

Lines 23 to 30 in 6e82793

	func getDefaultTmpDir() string {
	// first check the Temp env var
	// https://answers.microsoft.com/en-us/windows/forum/all/where-is-the-temporary-folder/44a039a5-45ba-48dd-84db-fd700e54fd56
	if val, ok := os.LookupEnv("TEMP"); ok {
	return val
	}
	return os.Getenv("LOCALAPPDATA") + "\\Temp"
	}

[sebsoto]

@Luap99 I can change the value to be in the temp folder so it actually becomes temporary.

[Luap99]

The change itself should be fine BUT

I think it would likely best to start with some high level overview of what you are going to change and how buildah on windows should work. We have very little windows expertise so any actual review will be very difficult us. Thus I am not sure how that would work out.
I am not strictly against it but I think this needs some actual plan first. How is going to do all that work and then also who is maintaining it going forward? (It would be best to keep that discussion on containers/buildah#4010).