Change ISO stream feature test and kvm user test for PPC

This patch removes X86 hardcoded tags from test XMLs in order to allow
run the tests in PPC machines.
It also increases the amount of memory used in User test xml, because
PPC only creates VMs with more then 128M.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>