[#57] services/object: Sign requests with session key

Use key storage in object services in order to sign requests with private
session key within user session.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/object/head/distributed.go

@@ -115,8 +115,8 @@ loop:
 					}
 				} else {
 					header = &remoteHeader{
-						key:  h.key,
-						node: addr,
+						keyStorage: h.keyStorage,
+						node:       addr,
 					}
 				}