Use OS specific file separator when printing out devc messages

[TrevCraw]

Dev mode prints out messages like below on Windows, which uses a mixture of \ and /. We should ensure these messages have the correct file separator at all times.

-v C:\Users\TREVORCrawford\Git\demo-devmode/target/liberty/wlp/usr/servers/defaultServer/bootstrap.properties:/config/bootstrap.properties

[ericglau]

Also consider when local paths are Windows and container paths are Linux style. e.g. ...usr\servers\defaultServer\something\bootstrap.properties:/config/something/bootstrap.properties