Refactor Barbican Secret to KMIP Object mapping

This patch refactors the mapping function used to convert Barbican Secrets into KMIP Objects. The KMIP Object used to store Opaque Secrets was changed from OpaqueObject to SecretData for better compatibility and adherance to the KMIP standard.

OpaqueObject was problematic because pykmip requires a value for the data type that is undefined in the KMIP spec. Additionally, some vendors don’t support Opaque objects at all, e.g. Fortanix DSM KMIP.

With this change, both Passphrase and Opaque Secrets are stored in the KMIP server using SecretData objects. This pach makes use of Application Specific Information to annotate the KMIP object with the Barbican Secret type it is storing. However, this annotation is purely informational. It may be useful when looking at objects in the KMIP device directly, but the deserialization of KMIP Objects continues to use the type information stored in the Barbican database.

This patch also deprecates the KMIP option [kmip_plugin] pkcs1_only in favor of two separate options in the same group: public_key_format and private_key_format. For backwards-compatibility, setting pkcs1_only=True overrides the values of both new options to use public_key_format=pkcs1 and private_key_format=pkcs1.