Don't auto-upgrade tiller in install_tiller
Summary
When testing a newer version of helm in a branch, the version of tiller was upgraded for the entire review cluster, causing pipeline failures
Steps to reproduce
Create a branch which uses a build image with a newer helm version
Current behavior
master and other branches will break due to the newer helm version
Expected behavior
master and other branches won't break
Relevant logs
Edited by Ian Baum