Resize/Migrate refactoring fixes and test cases

This patch will fix the construction of an scp command to be joined on
spaces. Also adds a parameter in driver.finish_migration to
_create_lpar_instance(), some refactoring that needed to be done in
order to launch the instance on the destination host. This patch fixes
Bug #1153599. This patch also address the tests cases for resize/migrate
functionality for PowerVM. Bug #1133058 is for tracking these test cases

Change-Id: I86c1b697fe5c7d6e4a6c689f75fd5cf737cef5d4