Use dev_server to determine the url of the devserver.

The dynamic_suite code assumed the devserver variable in the autotest
config was a string that represented the url for the devserver.
This is no longer a correct assumption as it can be a list of devservers.
This change modifies the dynamic_suite logic to use a DevServer instance
to tell it the URL it should use for the devserver.

BUG=chromium-os:26451
TEST=Unittests

Change-Id: I0bc63029630d9e884a23b16ccdf75da1756e6518
Reviewed-on: https://gerrit.chromium.org/gerrit/28447
Reviewed-by: Chris Masone <cmasone@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>
Commit-Ready: Chris Sosa <sosa@chromium.org>
diff --git a/global_config.ini b/global_config.ini
index f1db45b..3af9d0f 100644
--- a/global_config.ini
+++ b/global_config.ini
@@ -132,11 +132,9 @@
 dev_server: http://172.22.50.2:8082
 crash_server: http://127.22.50.2:8082
 sharding_factor: 1
-# The below should be %(dev_server)s/update/%%(name)s so that we'd fill in
-# the above value for dev_server when this config is parsed, but leave the
-# name field to be populated later.  Sadly, that doesn't parse.
-image_url_pattern: %(dev_server)s/update/%%s
-package_url_pattern: %(dev_server)s/static/archive/%%s/autotest/packages
+
+image_url_pattern: %s/update/%s
+package_url_pattern: %s/static/archive/%s/autotest/packages
 log_url_pattern: http://%s/tko/retrieve_logs.cgi?job=/results/%s/
 # Username and password for connecting to remote power control switches of
 # the "Sentry Switched CDU" type