Move pledge after getopt when we know whether the operation is reboot,

Move pledge after getopt when we know whether the operation is reboot,
powerdown, halt, or singleuser.  Before pledge, unveil access to
/dev/console, /etc/rc for singleuser entry, execute of /usr/bin/wall
to alert users, and creation of the fastboot and nologin files.  Also
conditionally allow execute of halt, reboot, or the shell depending on mode.
Believe all scenarios were tested -- please exercise this one a bit.