Change sampling ratio to 2% and add device config flag for sampling ratio adjustment.

Bug: 154373877
Test: adb shell device_config put permissions dangerous_permission_state_sampling_rate 1.0 &&
./out/host/linux-x86/bin/statsd_testdrive 10067
Change-Id: Idd16b38f015e071fb95f0daa628cdc41ea779947

Change-Id: I00bfa4abeb6a052237b245df368e24ed3da261d9