Added Private profile user type

adb root
adb shell
pm create-user --profileOf 0 --user-type android.os.usertype.profile.PRIVATE saumyap

^ This will return the user number of the new user (usually, 10). Start that user:

am start-user 10

Bug: 287976799
Test: atest com.android.server.pm.UserManagerTest#testPrivateProfile,
also created private profile manually via adb

Change-Id: Ibcdb14f33fc4d95c9d8d1cc6ffd10767b8352229