emulator test: add "rep ins" mmio access test

Add the test to trigger the bug that "rep ins" causes vcpu->mmio_fragments
overflow overflow while move large data from ioport to MMIO

Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>