bdr_init_copy enhancements

bdr_init_copy enhancements

Add --replication-sets command line parameter.
Specifies which replication sets to use for the new node. If not
specified the bdr_init_copy will check if all nodes in the bdr cluster
use same replication sets and use that one for the new node
automatically (instead of default). If the existing nodes don't all use
same replication sets it will throw error unless --replication-sets was
specified.

If the local data directory contains PostgreSQL data folder, check if
the system identifier is same as the system identifier of the remote
node. (GH #91)

When the remote node has multiple BDR activated databases make new
connections to all of them from the new local node. (GH #88)

Correctly set node_local_dsn for the new node.

Document -v option for increasing verbosity in --help output.