Treat date "from" filters as dates, not times

Without this, the existing tests fail when run on a system that's east of Greenwich.

(Namely, `rspec ./spec/models/rbac_spec.rb:719`.)

EDIT by @Fryguy: https://github.com/ManageIQ/manageiq/blob/27758d437b9a722136ad84aa5d962ec88eea8c94/vmdb/spec/models/rbac_spec.rb#L719