Allow use of local packages for developers to use when running tests.

The culprit behind the checksum logic not being run is client_logger in
autotest. I've changed client_logger such that it can be Site'ized
and added the necessary implementation in site_autotest to get this
working correctly for us.

The key issues were
1) client_logger ignored all requests for checksum files.
2) client_logger assumed you always wanted to re-tar code through
  the autotest workflow.

In addition, we should exclude packages from being wiped on every
installed hence the additional excluded dirs.

BUG=chromium-os:26561
TEST=Ran it, saved 30 seconds of 70 second tests.  Did not re-install
unnecessarily.

Change-Id: I7ac0a878f19296472f3b79e8cbe4cee641177215
Reviewed-on: https://gerrit.chromium.org/gerrit/17572
Reviewed-by: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
Commit-Ready: Chris Sosa <sosa@chromium.org>
3 files changed