When substitution of a templated entry attribute fails, we need to fall
back to a static definition of the attribute from the same entry. This
means, however, that ldap_attribute_to_rdatatype() will attempt to parse
an attribute value anyway and will be confused by the templating prefix,
thus reporting in named's logs:

unsupported operation: object class in resource record template DN
'idnsname=$NAME,idnsname=$ZONE.,cn=dns,$BASEDN' changed:
rndc reload might be necessary

Move recognition of a template attribute name to
ldap_attribute_to_rdatatype() so that a proper attribute class is
correctly derived and ignore templated attribute in the fallback code
if case that template expansion is failed.

Resolves: rhbz#1553512