Add connection test to deployment page

[ganiuszka]

Hello Everybody,

In issue https://github.com/bacularis/bacularis-app/issues/46 @sitemapxml proposed to add a connection test button (or deploy step with connection test) to test connection to remote hosts before starting the deployment process.

This issue is to keep this idea in the separate feature request.

Best regards, Marcin Haba (gani)