Until now, the secret service had a hard-coded TCP endpoint on port
1004. This change lets users specify arbitrary socket addresses.
* gnu/build/secret-service.scm (socket-address->string): New procedure,
taken from Shepherd.
(secret-service-send-secrets): Replace ‘port’ by ‘address’ and adjust
accordingly.
(secret-service-receive-secrets): Likewise.
* gnu/services/virtualization.scm (secret-service-shepherd-services):
Likewise.
(secret-service-operating-system): Add optional ‘address’ parameter and
honor it. Adjust ‘start’ method accordingly.
Change-Id: I87a9514f1c170dca756ce76083d7182c6ebf6578
f331a667d3