This commit also makes Face used inside NRD be adaptive to nfd.conf.
More specifically, it will use the same unix socket path as specified in
face_system.unix section. If this section is not present, it will use
the same tcp port as specified in face_system.tcp section. If tcp
section is also absent, nrd will abort execution.
Change-Id: I48f75ddf972f259055cd61824e3c228ca1d6a639
Refs: #2496