Prioritize Role over environment variables (nytimes#161)

* Update aws.go

* add also to subscriber

actually passing the email this time

fixing err declaration

[auth/gcp] looking up IAM email before fetching keyset

fixing audience check, using email in default credentials if it exist…

…s, using iam config email, if populated

adding identity helper func

using a build tag so we can use GAE std with auth/gcp

Adding "auth" and "auth/gcp" packages (nytimes#160)

[server/kit] Adding automatic Stackdriver logging for App Engine 2nd …

…generation runtime (nytimes#159)

* attempting to use stackdriver combined access/app logging in GAE 2nd gen runtime

* adding new gae log file

* setting traceid

* letting sd client do the jsoning

* fixing silliness

* adding missed project, var args ...

* no need to make the logger public

* docs update

* adding log levels

* removing unused key

* closing the sd logger at shutdown

* removing zone

expanding HTTP publishers to implement the MultiPublisher interface (n…

…ytimes#155)

* expanding HTTP publishers to implement the MultiPublisher interface

* adding tests