Fix dlogutil -d under Android Logger backend

Fix dlogutil -d under Android Logger backend

Util would keep reading as long as any data was in the buffer,
so if data came faster than it was processed then it would be
working indefinitely.

Now, it learns how many logs are present right at the start
by sending a get length request and only reads that many.

Change-Id: Idcfc7b10776ff93c85f16b335dad36d12bf5cd8e
Signed-off-by: Michal Bloch <m.bloch@samsung.com>