Turn on Rucio requests from DAS by default

[ericvaandering]

Only works within CERN, but you should use cms-rucio-int.cern.ch and cms-rucio-auth-int.cern.ch

[vkuznet]

I revisited work on DAS support for Rucio and found couple of issues which should be addressed:

• native request in Go to fetch Rucio token failed with rejection message that DN is not found. I think this is due to odd interaction with old Rucio apache frontend. To overcome this issue I enabled a mechanism to obtain token via curl system call
• the latency from Rucio server is quite large as requests takes 1.5 minutes to fetch the data, therefore I suggest we should make benchmarks and compare performance of Rucio with Phedex for the same dataset

Meanwhile, I tested new DAS version within k8s cluster and it works, see attached screenshot.