gddo-server: Group all flags into main package.

This CL moves the flags defined in database package into main and changes
them to exported variables.

Change-Id: I6c4c3287f20b506170375bbd30880d172fd39ea3
Reviewed-on: https://go-review.googlesource.com/24175
Reviewed-by: Alan Donovan <adonovan@google.com>
2 files changed