Vendor all dependencies w/ Godep

 * Remove `make updatedeps` from Travis build. We'll follow up with more
   specific plans around dependency updating in subsequent PRs.
 * Update all `make` targets to set `GO15VENDOREXPERIMENT=1` and to
   filter out `/vendor/` from `./...` where appropriate.
 * Temporarily remove `vet` from the `make test` target until we can
   figure out how to get it to not vet `vendor/`. (Initial
   experimentation failed to yield the proper incantation.)
 * Switch Travis install step to install stringer instead of `make
   updatedeps`

Everything is pinned to current master, with the exception of:

 * Azure/azure-sdk-for-go which is pinned before the breaking change today
 * aws/aws-sdk-go which is pinned to the most recent tag

The documentation still needs to be updated, which we can do in a follow
up PR. The goal here is to unblock release.

.gitignore

@@ -7,7 +7,6 @@ terraform.tfstate
 bin/
 modules-dev/
 pkg/
-vendor/
 website/.vagrant
 website/.bundle
 website/build

.travis.yml

@@ -5,7 +5,11 @@ language: go
 go:
   - 1.5
 
-install: make updatedeps
+# Need to ensure at least something remains in the install stanza to opt out of
+# Travis's built-in 'godep restore', which will fail Travis
+# See https://docs.travis-ci.com/user/languages/go#godep-support
+install:
+  - go get -u golang.org/x/tools/cmd/stringer
 
 script:
   - make test