Fix potentiel deadlock in audio VTS

The IDevice::debugDump method dumps debug info in a file descriptor.
Such file descriptor was previously the writing end of a pipe.

As the test is not multithreaded, if the dump was bigger than the pipe
buffer, a deadlock would occur.

With this patch, the test uses a file instead of a pipe. Thus write
will never block infinitely.

Test: run the corresponding vts test
Test: vts-tradefed r vts-hal-hidl -m VtsHalAudioV2_0Target

Bug: 34170075
Change-Id: I928cae712a1cb4411f907b3a9583014ba6486abc
Signed-off-by: Kevin Rocard <krocard@google.com>