The xml parser does not fill in defaults provided in the XSD when
validation is disabled. As a result, attributes like default-lazy-init
will not receive the value "default" but an empty string.

With this commit, BeanDefinitionParserDelegate now takes this into
account, checking default values against empty string as well as
"default".

As a consequence, default-lazy-init attribute should now work correctly
even when the XSD validation is disabled.

Issue: SPR-8335