adb_benchmark: allow mode on command line
adb_benchmark: allow mode on command line

Supported modes now are store, update, getkeys.
Fix a bug in getkeys counting.

sit/dht,weidezhang/dht,sit/dht,weidezhang/dht,weidezhang/dht,weidezhang/dht,weidezhang/dht,sit/dht,sit/dht,sit/dht