Fixed resource typing in Occi::Parser::Text

Occi::Parser::Text.resource is now using proper classes for
resource instances, i.e. Occi::Infrastructure::* instead of
a generic Occi::Core::Resource
Added spec for fixed resource typing
Simplified fix, using Occi::Core::Entity.new
Merge pull request #56 from arax/parser_fix_res

Fixed resource typing in Occi::Parser::Text