Notify: add pre_arm_gps_check flag

RGB LED will remain flashing blue when vehicle is disarmed and this
check has failed (i.e. false).

libraries/AP_Notify/AP_Notify.h

@@ -56,6 +56,7 @@ public:
         uint16_t baro_glitching     : 1;    // 1 if baro altitude is not good
         uint16_t armed              : 1;    // 0 = disarmed, 1 = armed
         uint16_t pre_arm_check      : 1;    // 0 = failing checks, 1 = passed
+        uint16_t pre_arm_gps_check  : 1;    // 0 = failing pre-arm GPS checks, 1 = passed
         uint16_t arming_failed      : 1;    // 1 if copter failed to arm after user input
         uint16_t save_trim          : 1;    // 1 if gathering trim data
         uint16_t esc_calibration    : 1;    // 1 if calibrating escs

libraries/AP_Notify/RGBLed.cpp

@@ -194,7 +194,7 @@ void RGBLed::update_colours(void)
         return;
     }
 
-    // solid green or flashing green if armed
+    // solid green or blue if armed
     if (AP_Notify::flags.armed) {
         // solid green if armed with GPS 3d lock
         if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D) {
@@ -234,32 +234,34 @@ void RGBLed::update_colours(void)
                     break;
             }
         }else{
-            // flashing green if disarmed with GPS 3d lock
-            // flashing blue if disarmed with no gps lock
+            // fast flashing green if disarmed with GPS 3D lock and DGPS
+            // slow flashing green if disarmed with GPS 3d lock (and no DGPS)
+            // flashing blue if disarmed with no gps lock or gps pre_arm checks have failed
+            bool fast_green = AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D_DGPS && AP_Notify::flags.pre_arm_gps_check;
             switch(step) {
                 case 0:
-                    if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D_DGPS) {
+                    if (fast_green) {
                         _green_des = brightness;
                     }
                     break;
                 case 1:
-                    if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D_DGPS) {
+                    if (fast_green) {
                         _green_des = _led_off;
                     }
                     break;
                 case 2:
-                    if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D_DGPS) {
+                    if (fast_green) {
                         _green_des = brightness;
                     }
                     break;
                 case 3:
-                    if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D_DGPS) {
+                    if (fast_green) {
                         _green_des = _led_off;
                     }
                     break;
                 case 4:
                     _red_des = _led_off;
-                    if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D) {
+                    if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D && AP_Notify::flags.pre_arm_gps_check) {
                         // flashing green if disarmed with GPS 3d lock
                         _blue_des = _led_off;
                         _green_des = brightness;
@@ -270,24 +272,24 @@ void RGBLed::update_colours(void)
                     }
                     break;
                 case 5:
-                    if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D_DGPS) {
+                    if (fast_green) {
                         _green_des = _led_off;
                     }
                     break;
 
                 case 6:
-                    if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D_DGPS) {
+                    if (fast_green) {
                         _green_des = brightness;
                     }
                     break;
 
                 case 7:
-                    if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D_DGPS) {
+                    if (fast_green) {
                         _green_des = _led_off;
                     }
                     break;
                 case 8:
-                    if (AP_Notify::flags.gps_status >= AP_GPS::GPS_OK_FIX_3D_DGPS) {
+                    if (fast_green) {
                         _green_des = brightness;
                     }
                     break;