Adds support to --user cur to locksettings binary.

Bug: 226643927
Test:  adb shell locksettings set-pin --user cur 4815162342 && adb shell locksettings clear --user current --old 4815162342
Test: atest FrameworksServicesTests # to make sure they didn't break

Change-Id: I6f755fe8124a42dcd33c2ce7d06f314f2d976c01