Add ssh_hba variable to turn on HBA for sshd

Gridengine (including OGS) requires host-based authentication
to use SSH rather than RSH for communication between the master
and the execution nodes.

This simply adds a variable 'ssh_hba' which can be set on 'yes'
in puppet to turn on HBA in sshd_config.

Key management will come in a different change.

Change-Id: Ibb49e71663fe2df2dd823b23f658e80a360c8a67
Merge "Add ssh_hba variable to turn on HBA for sshd" into production