Fix tf-operator presubmit failures by installing go manually

[richardsliu]

Presubmits were failing due to Go installation error:

Step 2/15 : ENV GOLANG_VERSION 1.8.3
---> Running in b613b7584fbe
Removing intermediate container b613b7584fbe
---> 966d561c20b7
Step 3/15 : RUN yum -y install go && yum clean all
---> Running in 3e92d32ce757
Loaded plugins: fastestmirror, ovl
Determining fastest mirrors
* base: mirrors.ocf.berkeley.edu
* extras: mirrors.ocf.berkeley.edu
* updates: mirror.sjc02.svwh.net
No package go available.
Error: Nothing to do
The command '/bin/sh -c yum -y install go && yum clean all' returned a non-zero code: 1
ERROR
ERROR: build step 0 "gcr.io/cloud-builders/docker" failed: exit status 1

Fix is to install Go (same version) manually.

This change is 

[richardsliu]

/assign @lluunn

[richardsliu]

/assign @johnugeorge

[johnugeorge]

/lgtm
/approve

[k8s-ci-robot]

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This pull-request has been approved by: johnugeorge

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[coveralls]

Coverage remained the same at 64.79% when pulling 9e153e4 on richardsliu:fix_presubmit into 4b54d94 on kubeflow:master.