[XEN][XEND][POWERPC] Don't ignore shadow memory requirement

[XEN][XEND][POWERPC] Don't ignore shadow memory requirement
We don't need a custom buildDomain() anymore but we do need to provide a
shadow memory calculation.

 - Create PPC_LinuxImageHandler class to implement
   getRequiredShadowMemory().
 - Derive prose builder from PPC_LinuxImageHandlerClass.
 - Drop configure() as it is not needed according to Jimi.

Signed-off-by: Ryan Harper <ryanh@us.ibm.com>
Signed-off-by: Jimi Xenidis <jimix@watson.ibm.com>
--HG--
extra : transplant_source : %09%80%DF%BA%E7F%80%5CQpNb%A1%BCF%03%CD%81PA