METER-388: allow API URL to be specified.

Summary: update setup_meter.sh to allow users to specify the API URL for Enterprise or Premium.  The ask here was originally to allow easy setup of a meter to talk to the premium staging.

Test Plan: tested on Ubuntu and OSX (premium).

Reviewers: busterb, thirty8super

Reviewed By: busterb

Differential Revision: http://phabricator.cid1.boundary.com/D3493
METER-323: add git hash to setup_meter.sh.