Dismiss keyguard right before startActivity

Screenshots suggest keyguard is in foreground when it failed,
dismiss the keyguard right before we start the activity to see if it
can fix the flakiness. And the test is now working even the screen is OFF.

Also removed the log as the original bug is fixed.

Test: cts-tradefed run cts-dev --module DevicePolicyManager --test com.android.cts.devicepolicy.MixedManagedProfileTest#testScreenCaptureDisabled

Fix: 34213859

Change-Id: I686ac9e3eeed6e4b33c3db2b0527647af6f7553e
2 files changed