Make snapshotctl also log to logd.

Since http://r.android.com/2994274, snapshotctl can be run by init.
Therefore, we need it to log to logd for better debuggability.

Bug: 311377497
Test: adb shell setprop sys.snapshotctl.map requested
Test: adb shell setprop sys.snapshotctl.unmap requested
Change-Id: I287ecf77d45fb9e6c44bea36e14d2624029afea5