webdav: Refactor XML normalisation for use with multistatusWriter tests.
webdav: Refactor XML normalisation for use with multistatusWriter tests.

This CL aims to provide a reusable XML normalisation mechanism across the
golden XML tests.

Change-Id: I39c957f1af4ce4672add38ea6a38c6a7c5f4f25c
Reviewed-on: https://go-review.googlesource.com/11032
Reviewed-by: Nigel Tao <58ae08b3356928ff9c67562b4719487d54fe8348@golang.org>

mckinney-subgraph/net,gomini/net,DramaFever/golang.org-x-net,flowlo/go-net,flowlo/go-net,golang/net,veliamsli/net,yangxianjun/net,subuk/net,dafyddcrosby/net,kiip/net,subuk/net,veliamsli/net,kiip/net,cmars/tools,muzining/net,w4ngyi/net,yangxianjun/net,cmars/tools,cesanta/goxnet,zabawaba99/net,raboof/net,albertjin/golang-net,mckinney-subgraph/net,albertjin/golang-net,muzining/net,dafyddcrosby/net,cmars/tools,gomini/net,cmars/tools,cesanta/goxnet,DramaFever/golang.org-x-net,zabawaba99/net,raboof/net,w4ngyi/net