Make the ipmitool provider properly use arguments in the ruby exec

Ruby needs the command line arguments to be in array format, otherwise it ends up execing:

`ipmitool "lan set 1"`

Which ipmitool doesn't like. Hard to debug though, because the debug output formats it into a string, which drops the quotes and array stuff. 

The provider still doesn't work yet, but at least it is executing the correct commands.

Next I'll work on parsing the output in a more robust manner, to get rid of these new `undefined method `strip' for nil:NilClass` errors.