docs/html: Properly generate ACL permissions into API reference

docs/html: Properly generate ACL permissions into API reference

The 'newapi.xsl' stylesheet was referencing non-existing paths to the
XML files holding ACL permission flags for individual APIs. Additionally
the 'document()' XSL function doesn't even allow concatenation of the
path as it was done via '{$builddir}/src..', but requires either direct
argument or use of the 'concat()' function.

This meant that the 'acls' variable was always empty and thus none of
our API documentation was actually generated with the 'acl' section.

Fix it by passing the path to the XML via an argument to the stylesheet
as the files differ based on which document is being generated.

Since the 'admin' API does not have ACL we need to handle it separately
now in the build system.

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>