Remove the reserved keyword check for config keys

[tbouron]

It makes sense to do this for metadata – we don't want to override brooklyn.enrichers or name. However, there shouldn't be restriction on keys within brooklyn.config.

For instance, this change allows the following blueprint:

services:
  - type: tomcat-server
    name: Foo
    brooklyn.config:
      cidrBlock: 10.0.0.0/24
      name: myVpc

whereas previously, name: myVpc would have been completely ignored by the composer.

[ahgittin]

LGTM