vendor: Bump installer to v0.12.0

Generated by manually updating Gopkg.toml and then running:

  $ dep ensure

with:

  $ dep version
  dep:
   version     : v0.5.0-31-g73b3afe
   build date  : 2019-02-08
   git hash    : 73b3afe
   go version  : go1.10.3
   go compiler : gc
   platform    : linux/amd64
   features    : ImportDuringSolve=false

Author: wking

Gopkg.lock

@@ -60,7 +60,7 @@ version="v1.4.7"
 
 [[constraint]]
   name = "github.com/openshift/installer"
-  revision = "7af6b141c34dd133f104b61b64c78d82e57f3d52"
+  version = "v0.12.0"
 
 [[constraint]]
   name = "github.com/openshift/generic-admission-server"