Update Instance Factory for Non-Resolvable Host

Update the Instance factory to ensure the default host is not a
resolvable host (otherwise, 404 errors are returned during testing that
are not expected).
Add Spec for Version7 connect_response_valid?

Update the Version7 spec to include tests for the
connect_response_valid? method.
Add connect_response_valid? Method to Version7

Update Version7 to include the connect_response_valid? method which
returns true only if the response corresponds to an HTTP 200 code.
Add Expected Response Fixtures for Testing

Add fixtures (txt and html) for specs.
Add Spec for Instance can_connect? Method

Update the Instance spec to include can_connect? method tests.
Add can_connect? Method to Instance

Update the Instance class to include a can_connect? method which
determines whether the Tomcat Manager instance is reachable and the
login credentials are acceptable.
Change All admin_ References to manager_

Update all files/specs/README to ensure that admin_username and
admin_password are instead referenced as manager_username and
manager_password, respectively, since 'manager' is the actual user that
interacts with the Tomcat Manager application (not 'admin').