audio: Update 'PauseSync' scenario in AudioStreamIoOutTest

According to the definition of the 'PAUSED' state
in StreamDescriptor.aidl, s/w (the client) stops
writing once the buffer is filled up. That means, it is
allowed for an output stream not to consume data
from the MQ while in the paused state, so allow that
in the test.

Also, update the state transition sequence in the test
to flush any data after making a burst while in the 'PAUSED'
state.

Bug: 328010709
Test: atest VtsHalAudioCoreTargetTest
Change-Id: Icb5fd02ca4ede63d7ae33613ab66cb96f3e6df29