Fix AppVeyor failing builds, by moving docker image url test to run on unix
systems only. The used paused image is a linux image only, not
available on Windows.
Due to https://github.com/tsenart/deadcode/issues/3 we can't specify
these consts on their own. This moves them into the _platform_test.go
files to avoid creating a package that only exposes a couple of values.
* Docker for Windows does not support ulimits
* Use filepath.ToSlash to test workdir
* Convert expected mount paths to system style
* Skip security-opt test on windows
- Windows does not support seccomp, and it's unclear which options are
available.
* Skip StartN due to lack of sigint
* docker: Use api to get image info on windows
* No bridge on windows
* Stop hardcoding /bin/
