detect ssh key accept prompts when logging into a new system

[cyrush]

Describe the bug

Before connecting via ssh, users need to have accepted the relevant ssh key for a connection.

This is usually done outside of VisIt, but there are cases where visit might use a different host name than a user would normally use to log in (for example: poodle, vs poodle.llnl.gov).

We should see if we can detect the yes/no challenge and show a dialog to a user when it occurs.