The top-level index should never be cached on the client since
it’s lightweight and points to the latest versions of the gr-app
resources. This was causing issues where users were seeing stale
versions of PolyGerrit because this page was being cached.
It should be noted that the _server_ should cache the index.html
file indefinitely, and that this change introduces a potentially
confusing parameter since “cache” is used both in the context of
the in-memory cache of the binary and also the user’s browser
cache.
Bug: Issue 4403
Change-Id: I70543aceedd5eea00ba9ee5123f16aaffb1f935c
a5979d5398