Adds checkSuccess and onFailure methods to poll feeds.

If checkSuccess(val) returns false onFailure is called instead of
onSuccess. If no handler for failures was created onException is called.
Existing entities' behaviour should remain the same. The HttpFeed has a
default success condition of 200 <= responseCode <= 399.

onError is deprecated in favour of onException, to make its purpose clear.
HttpFeed supports authentication

Supply username and password to HttpFeed buider. Uses httpcomponents'
standard mechanisms, so Brooklyn handles everything httpcomponents handles.
Extends HttpService to create servers requiring basic authentication.
Improve distinction between config keys and attributes in JBoss7Server
Enable AS7 management interface security by default

Adds MANAGEMENT_USER and MANAGEMENT_PASSWORD config keys to the AS7
entity. Username defaults to 'brooklyn', password to a random UUID.
Set NginxController SERVICE_UP feed to accept any HTTP response
Merge pull request #789 from sjcorbett/as7-security

HttpFeed authentication and AS7 security