Replace Glide with Golang Dep (#3522)

# Conflicts:
#	docs/developers.md

Author: juan-lee

Dockerfile

@@ -27,7 +27,7 @@ RUN git clone https://github.com/akesterson/shunit.git /tmp/shunit \
 WORKDIR /gopath/src/github.com/Azure/acs-engine
 
 # Cache vendor layer
-ADD Makefile test.mk versioning.mk glide.yaml glide.lock /gopath/src/github.com/Azure/acs-engine/
+ADD Makefile test.mk versioning.mk Gopkg.toml Gopkg.lock /gopath/src/github.com/Azure/acs-engine/
 RUN make bootstrap
 
 # https://github.com/dotnet/core/blob/master/release-notes/download-archives/2.1.2-sdk-download.md