EnvironmentVariableGroup blueprint now makes objects with unique names.

- updated specs to not specify names where it's not relevant to the test.

[#77942432]
Expanding coverage of "encrypted attribute" shared spec

- allowing for storage column of different name than the attribute (e.g., App#environment_json)
- allowing for varying salt column names
- adding coverage on salt length
- calling the shared spec from EnvironmentVariableGroup and App specs
- specifying the salt column in existing specs
- removing duplicate coverage from EnvironmentVariableGroup spec

[#77942432]
Created VCAP::CloudController::Encryptor::FieldEncryptor and specs

- to standardize how we encrypt fields in ccdb
- and to make it stupid simple for developers to encrypt fields

Subsequent commits will use FieldEncryptor across all models.

[#77942432]
Using FieldEncryptor for App#environment_json

[#77942432]
Using FieldEncryptor for EnvironmentVariableGroup#environment_json

[#77942432]
Using FieldEncryptor for ServiceAuthToken#token

[#77942432]
Using FieldEncryptor for ServiceBinding#credentials

[#77942432]
Using FieldEncryptor for ServiceBroker#auth_password

[#77942432]
Using FieldEncryptor for ServiceInstance#credentials

[#77942432]