debuggerd_client: improve error logging.

system_server is sometimes failing to dump with the following error:

    libdebuggerd_client: received packet of unexpected length from tombstoned: expected 128, received -1

Improve the logging to try to figure out what's going on.

Bug: http://b/114139908
Test: treehugger
Change-Id: Iee1bdc0891b9fc7bd80a330495ec22a530febddb