CBD-1040 Adapt warmup to not load all the keys with full eviction

When the full eviction is selected, we don't need to load all the
keys and their metadata during warmup. This means that the warmup
process skips "key_dump" phase and enters into
"loading_access_log" phase.

If the access log is corrupted or not found, then the warmup
process will enter into "loading_kv_pairs" phase.

Change-Id: Ia2a04e18d4f051ba5aac0a6b26d8e8f3073ca83c
Reviewed-on: http://review.couchbase.org/29702
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>