girocco: reserve the name 'bundle'

girocco: reserve the name 'bundle'

With personal mob area ref names etc. it's best to
avoid any possibility of collision or confusion so
just add 'bundle' to the list of reserved user names.

Additionally prevent any projects or user names that
end with '.bundle' from being created as well for
the same reason.

Finally make sure that all the reserved user names
are really getting a placeholder 0-byte sshkeys file
to help make sure they cannot be used.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>