cli: allow to pass sub commands to help as array

cli: allow to pass sub commands to help as array

Improves usabillity by allowing to pass a sub copmmand unquoted to
the help command, e.g.:

 # pveum help user delete

without this only a quoted version worked, e.g.:
 # pveum help "user delete"

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Acked-by: Wolfgang Bumiller <w.bumiller@proxmox.com>