[DPM] DO uses batch token to retrieve network logs, and can retrieve

the same batch many times

This allows DO to:
a) know that some logs were dropped (by trying with token and not
getting anything)
b) know how many logs were there in each batch (useful especially
for the dropped ones)
c) retry batch retrieval if it failed

Test: will be CTS tested once APIs unhidden
Bug: 29748723
Change-Id: I788359242e3b2a4cb638edb25e5db8b25646c29f