libchromeos: Improve VLOG(1) for async HTTP requests

In order to help with tracking HTTP requests and responses,
moved "noise" log messages from VLOG(1) to VLOG(2) and made sure
that each async request ID is logged before the request is dispatched
and also when response is received, the request ID is also logged so
it is easy to identify the matching request-response pairs.

BUG=None
TEST=`FEATURES=test emerge-link libchromeos`

Change-Id: I481ce25c8b3f2867ac8036c13bbee91bc8f6f838
Reviewed-on: https://chromium-review.googlesource.com/285744
Trybot-Ready: Alex Vakulenko <avakulenko@chromium.org>
Tested-by: Alex Vakulenko <avakulenko@chromium.org>
Reviewed-by: Vitaly Buka <vitalybuka@chromium.org>
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
2 files changed