conf: use virXMLNodeContentString for boot options parsing
conf: use virXMLNodeContentString for boot options parsing

Using XPath here doesn't add any benefit.

Signed-off-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>

fabianfreyer/libvirt,andreabolognani/libvirt,crobinso/libvirt,jfehlig/libvirt,eskultety/libvirt,crobinso/libvirt,andreabolognani/libvirt,olafhering/libvirt,nertpinx/libvirt,jardasgit/libvirt,olafhering/libvirt,libvirt/libvirt,andreabolognani/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,eskultety/libvirt,libvirt/libvirt,jardasgit/libvirt,crobinso/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt,libvirt/libvirt,crobinso/libvirt,andreabolognani/libvirt,olafhering/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,jfehlig/libvirt,nertpinx/libvirt,eskultety/libvirt,zippy2/libvirt,jardasgit/libvirt,eskultety/libvirt,eskultety/libvirt,nertpinx/libvirt,zippy2/libvirt,zippy2/libvirt,nertpinx/libvirt,jardasgit/libvirt,jfehlig/libvirt,fabianfreyer/libvirt