It is a bad idea to call gettext on an already-translated
string.  In cases where a string must be translated separately
from where it is exposed to xgettext, the gettext manual
recommends the idiom of N_() wrapping gettext_noop for
marking the string.

* src/internal.h (N_): Fix definition to match gettext manual.
* tools/virsh.c: (cmdHelp, cmdList, cmdDomstate, cmdDominfo)
(cmdVcpuinfo, vshUsage): Replace incorrect use of N_ with _.
(vshCmddefHelp): Likewise.  Mark C format strings appropriately.