Setting the correct PATH and pre-load the latest bbsim docker image to speed up the build

Change-Id: I558caf2b36bcd15cfc3e12b2716a7684a34a855b
diff --git a/tests/bbr.groovy b/tests/bbr.groovy
index 3b0f6f9..a86bc52 100644
--- a/tests/bbr.groovy
+++ b/tests/bbr.groovy
@@ -25,6 +25,7 @@
     stage('Build BBSim') {
       steps {
         sh """
+          docker pull voltha/bbsim:master
           make docker-build
         """
       }
@@ -32,6 +33,7 @@
     stage('Build BBR') {
       steps {
         sh """
+          export PATH=$PATH:/usr/lib/go-1.12/bin:/usr/local/go/bin:$GOPATH/bin
           make build-bbr
         """
       }