Add shardid information when no connection could be established

We have seen timeout related issues during copy commands. The error message is pretty naked on its own without good diagnostics information to understand which shard and therefore which machines it tried to connect to.

The log messages are:
https://github.com/citusdata/citus/blob/20c39fae9a9b7eb9207f96c025473e5f03e326b9/src/backend/distributed/commands/multi_copy.c#L892
https://github.com/citusdata/citus/blob/20c39fae9a9b7eb9207f96c025473e5f03e326b9/src/backend/distributed/commands/multi_copy.c#L3486

Adding the shardid in the detail might be of great insight for anyone running into this issue in production