Using dep as go dependencies management

- Using dep as go depedencies management
- Updating imports and code to comply to updated dependencies
- Updating Makefile to use dep instead of glide
- Updating Travis CI to also use dep instead of glide

This fixes the bug where reclaimPolicy was not taken into account by the
external provisioner (upgrading to latest version fixes it)

.travis.yml

@@ -1,11 +1,10 @@
 language: go
 go:
-- '1.8'
+- '1.10.x'
 sudo: false
 
 before_install:
-- go get -v github.com/Masterminds/glide
-- cd $GOPATH/src/github.com/Masterminds/glide && git checkout e73500c735917e39a8b782e0632418ab70250341 && go install && cd -
+  - curl https://raw.githubusercontent.com/golang/dep/master/install.sh | sh
 
 install:
   make vendor
@@ -30,4 +29,4 @@ deploy:
   skip_cleanup: true
   on:
     tags: true
-  go: 1.8
+  go: 1.10.x