Validate providers after creating all providers

* Speeds up setup_providers a bit by using the optimization used in
  clear_providers: All providers are added first, then validated. This
  buys a little time for the first provider that was added to get started
  on its collection
* I tried to keep the setup functionality separate, but gave up.
validate/_do_stats_match are more opportunitic and less verbose

* validate runs _do_stats_match before initiating a refresh in case the stats
  are already matched
* _do_stats_match logging tweaked a little bit; the debug statements that were
  removed were distracting, but the actual stats match log line got promoted
  to INFO.
s/browser/sel/

`pytest_selenium == pytest.sel == sel`
Merge pull request #508 from seandst/setup-providers-speedup

Setup providers speedup