mkcloud help split into separately displayable sections

  mkcloud (-h | --help | usage) - 10kft overview
  mkcloud (help-cmds | help-vars) - should be obvious
  mkcloud help - full help (usage + cmds + vars)

usage output goes to stdout or stderr based on whether it's
being displayed by request or pilot error.
mkcloud: dedup help on commands a bit
mkcloud: dedup help on commands a bit more
mkcloud: check variables before permissions

no need to demand root when the invocation is busted anyway.

while i'm at it, duplicate descriptions of $cloudsource
and $nodenumber are gone.
mkcloud: stop using nonexistent variable

the mystical $h1 appeared in b95bcb0543eab2299a343867ff37dd0a370a7bdf,
looks like copy/paste leftover.
mkcloud: dedup error reporting with a function

error messages go to stderr as dog intended.
mkcloud: make sure all errors go to stderr
mkcloud: dedup expansion of aggregate commands
mkcloud: dead variable

leftover from 9cb10555fe236a2089b99fa3c3c112c425f75516
mkcloud: pvlist need not be global