Fix the cts-on-gsi#testLockTaskAfterReboot&&testLockTaskAfterReboot_tryOpeningSettings

Test:run cts-on-gsi -m CtsDevicePolicyManagerTestCases -t com.android.cts.devicepolicy.MixedDeviceOwnerTest#testLockTaskAfterReboot
run cts-on-gsi -m CtsDevicePolicyManagerTestCases -t com.android.cts.devicepolicy.MixedDeviceOwnerTest#testLockTaskAfterReboot_tryOpeningSettings

Cause:LockTask is not ready after the device reboot while the test continues.

Solution:  Wait all broadcast queues are idle after reboot before continue the test.

Bug:151796574
Change-Id: I6f652c3295b1d37c297e6e0d14287a56f8a22d6c