Use toplevel CMakeLists.txt

Change-Id: Icf8436cf3e24b8754133bf8683b633839dc77230
Reviewed-on: http://review.couchbase.org/28729
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>