WPAR plugin: Refactored read and init callbacks.

WPAR plugin: Refactored read and init callbacks.

* The CPU information has been coverted to derive.
* The memory and cpu/load acquiring has been broken out of the main read
  method.
* The plugin will now keep the memory is acquired last time around for the next
  call to read(). It is cleaned up in the new shutdown() function. This should
  minimize the number of calls to realloc().