There si no IPMI support in Windows in this implementation

IPMI management tools are not available in windows so all linux-specific
parts have to be executed only on supported platforms.
Fixed the test of node platform together with the testing of the ipmi
tools availability.
Fixed the unless test to avoid trying to install the ipmitool package
if node[:platform] is windows or it is already installed.
Fixed the unless test to avoid trying to set IPMI address and user
if node[:platform] is windows or it is already installed.
Merge pull request #50 from ociuhandu/pull-req-release-pebbles-master-58a2078e8676eb14d4439f36e1ad3e1385f0a21b

https://github.com/crowbar/barclamp-ipmi/pull/50

Merged by devtool for VictorLowther