Autocomplete disconnect command

I found this useful when I have many ADB devices (especially cuttlefish
or VMs).

Test: manual
Change-Id: Ie7bfec0b55c76cfa0c850b95a8028e548a7393d3
diff --git a/adb.bash b/adb.bash
index 8fc343f..ad62eba 100644
--- a/adb.bash
+++ b/adb.bash
@@ -77,8 +77,7 @@
             COMPREPLY=( $(compgen -W "$OPTIONS $COMMAND" -- "$cur") )
             ;;
         OPT_SERIAL_ARG)
-            local devices=$(command adb devices 2> /dev/null | grep -v "List of devices" | awk '{ print $1 }')
-            COMPREPLY=( $(compgen -W "${devices}" -- ${cur}) )
+            _adb_devices
             ;;
         COMMAND)
             if [[ $i -eq $COMP_CWORD ]]; then
@@ -86,6 +85,9 @@
             else
                 i=$((i+1))
                 case "${cur}" in
+                    disconnect)
+                        _adb_devices
+                        ;;
                     install)
                         _adb_cmd_install "$serial" $i
                         ;;
@@ -118,6 +120,12 @@
     return 0
 }
 
+_adb_devices() {
+    local devices=$(command adb devices 2> /dev/null | grep -v "List of devices" | awk '{ print $1 }')
+    COMPREPLY=( $(compgen -W "${devices}" -- ${cur}) )
+    return
+}
+
 _adb_cmd_install() {
     local serial i cur where