agent crashes if vereign_ca key/cert not found

2019/11/02 08:08:02 client.go:768: Error: rpc error: code = Canceled desc = grpc: the client connection is closing
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x1061f0b8]

instead of exiting gracefully