Add tGroup based unxsVZ pre-start container file system modification

[Dylan]

unxsVZ must provide for optional tGroup based system for configuring container files before a new container is started. The same system can be used to add files.

An example that is required ASAP by SLA customer is for sendmail.cf MASQUERADE modifications based on container hostname.

This system can be extended later for group update operations to configure running containers.

Probably should use tTemplate for storing configuration files with variable syntax and use openisp libtemplate functions.