bash-completion: setpriv --securebits argument can be comma separated list

Make the option argument suggestion to match with what is allowed.  In same
go tidy shell code a little bit.

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

bash-completion/setpriv

@@ -46,10 +46,23 @@ _setpriv_module()
 			return 0
 			;;
 		'--securebits')
-			local SBITS
-			SBITS="noroot noroot_locked no_setuid_fixup no_setuid_fixup_locked keep_caps_locked
-			-noroot -noroot_locked -no_setuid_fixup -no_setuid_fixup_locked -keep_caps_locked"
-			COMPREPLY=( $(compgen -W "$SBITS" -- $cur) )
+			local prefix realcur SBITS_ALL SBITS WORD
+			realcur="${cur##*,}"
+			prefix="${cur%$realcur}"
+			SBITS_ALL="
+				{+,-}keep_caps_locked
+				{+,-}noroot
+				{+,-}noroot_locked
+				{+,-}no_setuid_fixup
+				{+,-}no_setuid_fixup_locked
+			"
+			for WORD in $SBITS_ALL; do
+				if ! [[ $prefix == *"$WORD"* ]]; then
+					SBITS="$WORD ${SBITS:-""}"
+				fi
+			done
+			compopt -o nospace
+			COMPREPLY=( $(compgen -P "$prefix" -W "$SBITS" -S ',' -- $realcur) )
 			return 0
 			;;
 		'--selinux-label')