Fix 1362 & 1366; cache less to improve correctness and performance
"MVC5 Bug: Views are not compatible with Virtual Path Providers"
- https://aspnetwebstack.codeplex.com/workitem/1362
- Should never cache HostingEnvironment.VirtualPathProvider; this property
may change at any time.
- This bug is a regression from MVC4.

"MVC bug: Bad performance of views if ViewEngines.Engines is initialized
without HttpContext"
- https://aspnetwebstack.codeplex.com/workitem/1366
- ViewEngines.Engines may be read before HttpContext.Current is initialized,
leading to inefficient use of the NullViewLocationCache instance.