Ambari upgrade would fail for all Ambari view servers.
Steps to reproduce:
1. Install Ambari 2.5.2 and setup it as view server. (it you don't set up it up as view server also it fails)
2. now install 2.6.0
3. run ambari-server upgrade
it fails out with below exception.
For some reason we are checking cluster_version table entries and throwing up above exception.