rcontrol_paramiko: send noop packets every 10 seconds

This makes sure that the connection is up and running and also makes sure
that firewalls or other gateway's don't timeout our SSH connections.
tool: convert "-d REPO" path to absolute path

Not all commands (e.g. "audit") fully worked with relative
repository paths.
poni: keyword to get script path and more information in file not found situation

Added a way to expand the directory from which a script was ran inside itself.
This is now possible with "$script_path" variable which will be rendered to a value
which is full path to the script with script filename removed.

Also added more verbosity when file is not found in update-config
cloud_libvirt: default to diskcache=none

"none" gives the best performance and reliability by default.  It also
allows VMs to be live-migrated across different hosts.  "writeback" is
faster in some workloads, but does not support live migration and may
not be as reliable in all situations.
rcontrol_paramiko: retry channel opening on failure

Retries "SSHException: Unable to open channel." failures in the
connecting phase in case transport or channel opening fails.