Use REACTANT_DEFAULT_DEVICE to set default device ID with env var

Author: giordano

src/xla/Client.jl

@@ -13,4 +13,5 @@ function get_device end
 function get_addressable_device end
 function platform_name end
 
-default_device(client::AbstractClient) = first(addressable_devices(client))
+default_device(client::AbstractClient) =
+    addressable_devices(client)[something(tryparse(Int, get(ENV, "REACTANT_DEFAULT_DEVICE", "1")), 1)]