IPMI support completion

[aquette]

A few things are still missing, to complete IPMI support:

• [ ] IPMI scan should first do an "ipmi ping", prior to doing an actual ipmi open. Refer to http://www.gnu.org/software/freeipmi/manpages/man8/ipmiping.8.html This is applicable to both nut-ipmipsu and nut-scanner
• [ ] IPMI driver still does not handle commands (on, off, sw off) Refer to http://www.gnu.org/software/freeipmi/manpages/man8/ipmipower.8.html

Lower priority:

• [ ] better NUT IPMI back-ends interface (create a NUT IPMI API)
• [ ] Allow runtime selection (beside compile time) of the IPMI backend used
• [ ] 2nd IPMI back-end implementation, beside of FreeIPMI (ipmiutil or ipmitool)
• [ ] Rename to nutdrv-ipmipsu (or simply nutdrv-ipmi?)

Note on ipmiutil: It provides transparent IPMI command-level access for in-band and out-of-band. Using the ipmi_sample.c in the devel package does support FRU, SDR, etc., so that shows how this is used, and could be compiled as a library as well. And there is an ipmi_sample_evt.c for handling events. Andy Cress also proposed some help and is interested in feedback.

Note on ipmitool: Used at least on Opengear systems.

[zanchey]

It would be great if the PSU support could be added as well.