buffet: Implicitly define minimalRole in command definition file

Buffet still set minimalRole to 'user' even if value is omitted.

BUG=brillo:808
TEST=`FEATURES=test emerge-gizmo buffet`

Change-Id: I8d0ca7a2b38fd265a0f4ac468ed8ee3e0550a09f
Reviewed-on: https://chromium-review.googlesource.com/274233
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>

buffet/etc/buffet/gcd.json

diff --git a/buffet/etc/buffet/gcd.json b/buffet/etc/buffet/gcd.json
index dae09f9..ac85f6b 100644
--- a/buffet/etc/buffet/gcd.json
+++ b/buffet/etc/buffet/gcd.json
@@ -1,6 +1,7 @@
 {
   "base": {
     "updateBaseConfiguration": {
+      "minimalRole": "manager",
       "parameters": {
         "localDiscoveryEnabled": "boolean",
         "localAnonymousAccessMaxRole": [ "none", "viewer", "user" ],
@@ -10,16 +11,19 @@
     },
 
     "reboot": {
+      "minimalRole": "user",
       "parameters": {},
       "results": {}
     },
 
     "identify": {
+      "minimalRole": "user",
       "parameters": {},
       "results": {}
     },
 
     "updateDeviceInfo": {
+      "minimalRole": "manager",
       "parameters": {
         "description": "string",
         "name": "string"