Move dev_server_wrapper from crostestutils.lib to chromite.lib

Scripts such as cros flash can use dev_server_wrapper. crostestutils
already imports chromite.

BUG=None
TEST=None
CQ-DEPEND=CL:181048

Change-Id: Ide5890e69e0ec13ccce449a412ac0e782c340a79
Reviewed-on: https://chromium-review.googlesource.com/181049
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Yu-Ju Hong <yjhong@chromium.org>
Tested-by: Yu-Ju Hong <yjhong@chromium.org>
6 files changed