Change getUid before turning screen off

getUid is based on ADB shell command execution and device should be connected
to host. However, there're turnScreenOff during test and it causes device
getting suspend state. In that case, the test cannot complete properly due to
ADB disconnection. Therefore, getUid should be uppper turnScreenOff.

Bug: b/143046081
Test: run cts -m CtsStatsdHostTestCases -t android.cts.statsd.validation.ValidationTests#testPartialWakelockDuration
Change-Id: Ic4264a457544515451225a71a36058ebc69a7ca4
Merged-In: Id71f08d067d463e78a9dccb6b55dfab6c768888b