zdtm: add tests which can be executed in a new user namespace

Sockets tests are excluded, because SO_RCVBUFFORCE and SO_SNDBUFFORCE
are protected by CAP_NET_ADMIN

tty*, pty* are excluded, because TIOCSLCKTRMIOS protected by
CAP_SYS_ADMIN

*ghost, *notify, *unlink* are excluded, because linkat(AT_EMPTY_PATH)
are protected by CAP_DAC_READ_SEARCH
xxx
travis