go-plugin quick and dirty spike

[lukaso]

Notes / Findings

• Logging has to be directed to Stderr as the server will otherwise fail. See client Error:Unrecognized remote plugin message... hashicorp/go-plugin#199
• The server must handle graceful shutdowns, or hops stays running.
• go-plugin has a capability to reconnect to a process, but this was not investigated.
• Uses the net/rpc version, not the gRPC version.
• Shared interface should live in hops, but obviously changes to this interface would have to be dealt with as and when.
• Only useful for local communications.

[lukaso]

Hashicorp Plugin spike