rgw: Verify key id before sending to Barbican

rgw: Verify key id before sending to Barbican

`request_key_from_barbican` is called with a raw user-defined key id.
To prevent issues like path injection match against a UUID4 regex
first. Add this check close to the Barbican calls, as other KMS
backends have other key format definitions.

Barbican secret ids are defined as "uuid" and matched against Python's
UUID 4 parser.

Signed-off-by: Marcel Lauhoff <marcel.lauhoff@clyso.com>
On-behalf-of: SAP marcel.lauhoff@sap.com