Add a command to modify node hw_info data

If users need to move, e.g., a network card from one system to another, they
need to tell Razor that that is happening. To facilitate this, we need a
command that lets users selectively remove, add, or modify entries in the
nodes hw_info table.

This implements that, as a single atomic "set hw_info to" operation.  In cases
where partial change is desired, this can be implemented by modifying the data
read from the server -- since there is, in essence, only administrative change
performed to this data, we have no significant edit conflict risk.

https://tickets.puppetlabs.com/browse/RAZOR-69
Signed-off-by: Daniel Pittman <daniel@rimspace.net>