Migrate from glide to dep for dependency management (openshift#1670)

* dep init

* Resolve conflict for code.cloudfoundry.org/lager
  code.cloudfoundry.org/lager is required to be at 0bfa98e by
  github.com/pivotal-cf/brokerapi
  https://github.com/pivotal-cf/brokerapi/blob/35946a0079bda144d0c9ed68df36899451f90209/Gopkg.toml#L26

* Require code generators and build tools
  I had to change the constraint for repo-infra from a pinned revision
  to latest on master. I was running into dependency hell otherwise. Can revisit if
  necessary.

* Sync vendor to Gopkg.lock

* Ignoring large doc files in GoLLRB

* Validate vendor and dep config during build

* Add test-dep target
  Validates that a downstream consumer of our client library can use dep
* Add verify-vendor target
  Validates that what is in vendor/ is in sync with Gopkg.lock
* Install dep in the docker build image

* Update relevant glide usage to dep

We cannot completely remove glide because we are using
`glide nv`. If we had a requirement of Go 1.9+ maybe that could
be dropped, since the go tools in that version don't include
vendor anymore with `./...`, but until then it needs to stay.

* Remove glide config files in favor of dep's

* Skip dep's cache during href checking

* Remove native dep targets

They don't work because GOPATH is redefined in the Makefile
So people will just have to rely on the docker, or install dep themselves.

Author: carolynvs

Diff for: .gitignore

@@ -10,7 +10,6 @@ bin/**
 coverage.html
 .idea/
 .DS_Store
-.glide
 .scBuildImage
 .init
 .generate*
@@ -21,3 +20,7 @@ contrib/build/*/tmp/*
 .kube
 .var
 .vscode
+vendor/github.com/petar/GoLLRB/doc/*
+contrib/examples/consumer/Gopkg.lock
+contrib/examples/consumer
+contrib/examples/vendor/*

Diff for: .travis.yml

@@ -4,7 +4,7 @@ services:
 - docker
 cache:
   directories:
-  - .glide
+    - $GOPATH/pkg/dep
 script:
 - make verify build build-integration build-e2e test images svcat
 deploy: