[PATCH for 7.4.0] conf: Avoid double indentation of <metadata/> element

[Bjoern Walk]

Michal Privoznik <mprivozn at redhat.com> [2021-05-25, 09:32AM +0200]:
> There was a recent change in libxml2 that caused a trouble for
> us. To us, <metadata/> in domain or network XMLs are just opaque
> value where management application can store whatever data it
> finds fit. At XML parser/formatter level, we just make a copy of
> the element during parsing and then format it back. For
> formatting we use xmlNodeDump() which allows caller to specify
> level of indentation. Previously, the indentation was not
> applied onto the very first line, but as of v2.9.12-2-g85b1792e
> libxml2 is applying indentation also on the first line.
> 
> This does not work well with out virBuffer because as soon as we
> call virBufferAsprintf() to append <metadata/> element,
> virBufferAsprintf() will apply another level of indentation.
> 
> Instead of version checking, let's skip any indentation added by
> libxml2 before virBufferAsprintf() is called.
> 
> Note, the problem is only when telling xmlNodeDump() to use
> indentation, i.e. level argument is not zero. Therefore,
> virXMLNodeToString() which also calls xmlNodeDump() is safe as it
> passes zero.
> 
> Signed-off-by: Michal Privoznik <mprivozn at redhat.com>

Tested-by: Bjoern Walk <bwalk at linux.ibm.com>

But like Daniel said, this now breaks for older libxml2 versions.
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