[tests] Check allowed errors when invoking registry_load_all() method
[tests] Check allowed errors when invoking registry_load_all() method

Some warnings when loading all plugins should be allowed in the test. Mainly,
when a directory does not contain any plugin or when a plugin is not provided
with a required configuration.

In these cases, test should not fail.

jasuarez/grilo,GNOME/grilo,MathieuDuponchelle/grilo,jasuarez/grilo,MathieuDuponchelle/grilo,kyoushuu/grilo,jasuarez/grilo,kyoushuu/grilo,MathieuDuponchelle/grilo,kyoushuu/grilo,grilofw/grilo,grilofw/grilo,kyoushuu/grilo,GNOME/grilo,grilofw/grilo