Support rotated logs.

cros_logging will look at /var/log/messages, /var/log/messages.1, /var/log/messages.2 etc when searching for the last boot or a string.

Change-Id: I726a69478a38bd35a5bb92a48a20723992b0a6a2

BUG=chromium-os:12791
TEST=
TBR=dalecurtis@chromium.org
2 files changed