[autotest] Put dev server error strings in exceptions

We've been ignoring error messages coming back from the dev server.
Strip out the HTML that comes in (some of) them and wrap them
in exceptions.

BUG=chromium-os:30279
TEST=unit
TEST=use atest suite create to run a suite that doesn't exist on build that doesn't exist.

Change-Id: I86b149610bf54334cdca12836a078ab874c818b2
Reviewed-on: https://gerrit.chromium.org/gerrit/22315
Commit-Ready: Chris Masone <cmasone@chromium.org>
Reviewed-by: Chris Masone <cmasone@chromium.org>
Tested-by: Chris Masone <cmasone@chromium.org>
diff --git a/server/cros/control_file_getter.py b/server/cros/control_file_getter.py
index 2f83538..4393c6b 100644
--- a/server/cros/control_file_getter.py
+++ b/server/cros/control_file_getter.py
@@ -193,12 +193,12 @@
         |self._dev_server|.  Populates |self._files| with that list
         and then returns paths (under the autotest dir) to them.
 
-        @return A list of control file paths.  None on failure.
+        @return A list of control file paths.
         @throws NoControlFileList if there is an error while listing.
         """
         try:
             return self._dev_server.list_control_files(self._build)
-        except urllib2.HTTPError as e:
+        except dev_server.DevServerException as e:
             raise error.NoControlFileList(e)
 
 
@@ -214,5 +214,5 @@
         """
         try:
             return self._dev_server.get_control_file(self._build, test_path)
-        except urllib2.HTTPError as e:
+        except dev_server.DevServerException as e:
             raise error.ControlFileNotFound(e)