shell-completion,man: beef up chassis completions and description

Parameters to hostnamectl command are not optional and should not be marked
as such in the man page.

(cherry picked from commit 1ed7749564)
(cherry picked from commit ba838f7f9b)

shell-completion/bash/hostnamectl

@@ -39,6 +39,7 @@ _hostnamectl() {
                 [STANDALONE]='status'
                      [ICONS]='set-icon-name'
                       [NAME]='set-hostname'
+                   [CHASSIS]='set-chassis'
         )
 
         for ((i=0; i < COMP_CWORD; i++)); do
@@ -50,6 +51,8 @@ _hostnamectl() {
 
         if [[ -z $verb ]]; then
                 comps=${VERBS[*]}
+        elif __contains_word "$verb" ${VERBS[CHASSIS]}; then
+                comps='desktop laptop server tablet handset watch vm container'
         elif __contains_word "$verb" ${VERBS[STANDALONE]} ${VERBS[ICONS]} ${VERBS[NAME]}; then
                 comps=''
         fi