Fix dataproxy_test.go tests
Fix dataproxy_test.go tests

This change fix dataproxy_test.go tests that was failing with:

pkg/api/dataproxy_test.go:17: not enough arguments in call to NewReverseProxy
pkg/api/dataproxy_test.go:39: not enough arguments in call to NewReverseProxy
FAIL	_/home/ubuntu/grafana/pkg/api [build failed]

grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana,grafana/grafana