APIGateway does not send auth headers when `--http_basicauth` flag is set in Mesos

[iderdik]

After turning on basic auth, the APIgateway no longer sends traffic to leader properly and fails.

I get the basic auth prompt and log in successfully but then all calls to /master/state return a 500 error

cc @matthewdfuller @ddragosd

[ddragosd]

@iderdik the Gateway configuration needs to be updated to include the Basic Auth header when proxying to Mesos. I will take a look at the Lua scripts.

[iderdik]

Thanks @ddragosd please let me know if you need any more info or testing.

[iderdik]

@ddragosd bump