Fix/handle faults during create shell

[Jbekker]

This is to resolve two open issues, #176 and #41

1. Adds error handling to ParseOpenShellResponse so that users have the ability to retry opening a shell when this fails.
2. It makes the private err field on the command accessible, similar to c.exitCode.

[anurag5sh]

@masterzen this would solve some long standing issues in packer

[masterzen]

Sorry for the late review, I was abroad with few network access.
This looks correct and I'm inclined to merge the PR, but would you mind taking a look at my suggestions?
Thanks!

[Jbekker]

Since the ParseOpenShellResponse and ParseExecuteCommandResponse functions are now almost identical, we could also extract the common parts into it's own function so you get something like this:

What are your thoughts on that?

func parseResponse(response string, expectedAction, idXPath, errorMsg string) (string, error) {
	...
}

func ParseOpenShellResponse(response string) (string, error) {
	return parseResponse(
		response,
		"http://schemas.xmlsoap.org/ws/2004/09/transfer/CreateResponse",
		"//rsp:ShellId",
		"error during shell creation",
	)
}

func ParseExecuteCommandResponse(response string) (string, error) {
	return parseResponse(
		response,
		"http://schemas.microsoft.com/wbem/wsman/1/windows/shell/CommandResponse",
		"//rsp:CommandId",
		"error during command execution",
	)
}

[masterzen]

Since the ParseOpenShellResponse and ParseExecuteCommandResponse functions are now almost identical, we could also extract the common parts into it's own function so you get something like this:

What are your thoughts on that?

Indeed, even better!
Would you mind adding a commit?
If not, we can merge as is.

[Jbekker]

Sure, I'll create a commit for this when I can. Probably tomorrow morning.

[anurag5sh]

are we good to merge this? @Jbekker

[Jbekker]

are we good to merge this? @Jbekker

We are! @masterzen, please take a look.

[masterzen]

LGTM, let's merge