server.hosts.remote: When install server is not available, retry

Rather than giving up and throwing a hard to understand
exception to users when the install server code can't reach
the install server, retry every install_timeout / 100 seconds.

If after install_timeout / 10 we still could not reach
the server, then throw an easier to understand error
(Could not contact the install server).

CC: Rudá Moura <rmoura@redhat.com>
Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>