Scope ModelHelpers to spec/unit/models

[#72354980]

Signed-off-by: Joseph Palermo <jpalermo@pivotallabs.com>
Include BrokerApiHepler in specs that need it

[#72354980]

Signed-off-by: Joseph Palermo <jpalermo@pivotallabs.com>
Remove unused include of VCAP::CloudController in spec helper

[#72354980]

Signed-off-by: Joseph Palermo <jpalermo@pivotallabs.com>