Changed dpm shell commands to use 'cmd device_policy'

Added the missing commands to DevicePolicyManagerServiceShellCommand and
changed 'adb shell dpm' to call 'adb shell cmd device_policy'

Fixes: 173381875
Test: atest com.android.bedstead.nene.devicepolicy.DevicePolicyTest
Test: atest com.android.bedstead.nene.devicepolicy.ProfileOwnerTest
Test: atest com.android.bedstead.nene.devicepolicy.DeviceOwnerTest
Test: manually tested the migrated commands
Change-Id: Id86382f11cf8197230ef62c33961e01b0b541358