rpc_test: Use injected connect error
rpc_test: Use injected connect error

Currently the error to connect is coded as a part of generic (at the
test level) rpc_socket_impl, but error-injector is some better place.

Signed-off-by: Pavel Emelyanov <c9a32589e048e044184536f7ac71ef92fe82df3e@scylladb.com>

scylladb/seastar,syuu1228/seastar,scylladb/seastar,syuu1228/seastar,syuu1228/seastar,scylladb/seastar