When `-s` is not specified, there is no need to ask if there is a plugin
with the specified name.
This speeds up unit tests dramatically since they don't need to wait the
timeout period for each call to `graphdriver.New`.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Upstream-commit: 3b16cb15b496edc3dc080560c7189e06e19c5343
Component: engine