[autotest] Honor --image over host attr when determining pkg fetch location

Existing tests use a command-line option to autoserv to determine where to
fetch testing packages from.  The new dynamic suite stuff uses a host-attribute.
We need to check the old way first and use the value we find there, or else
old-style test suites will fail.

BUG=chromium-os:26805
TEST=manual

Change-Id: I5c26bc72f6756fefc9836869db24ea0188b04706
Reviewed-on: https://gerrit.chromium.org/gerrit/16540
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Ready: Scott Zawalski <scottz@chromium.org>
Reviewed-by: Scott Zawalski <scottz@chromium.org>
Tested-by: Scott Zawalski <scottz@chromium.org>
1 file changed