Try to get the Kobo codename from the env first

My batch of startup script tweaks should ensure PRODUCT is always
exported.
Leave the fallback in place, to avoid blowing up in weird corner-cases I
haven't thought about.

frontend/device/kobo/device.lua

@@ -108,9 +108,14 @@ function Kobo:init()
 end
 
 function Kobo:getCodeName()
-    local std_out = io.popen("/bin/kobo_config.sh 2>/dev/null", "r")
-    local codename = std_out:read()
-    std_out:close()
+    -- Try to get it from the env first
+    local codename = os.getenv("PRODUCT")
+    -- If that fails, run the script ourselves
+    if not codename then
+        local std_out = io.popen("/bin/kobo_config.sh 2>/dev/null", "r")
+        codename = std_out:read()
+        std_out:close()
+    end
     return codename
 end