s390x: Test effect of storage keys on some instructions

Some instructions are emulated by KVM. Test that KVM correctly emulates
storage key checking for two of those instructions (STORE CPU ADDRESS,
SET PREFIX).
Test success and error conditions, including coverage of storage and
fetch protection override.
Also add test for TEST PROTECTION, even if that instruction will not be
emulated by KVM under normal conditions.

Signed-off-by: Janis Schoetterl-Glausch <scgl@linux.ibm.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Acked-by: Janosch Frank <frankja@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>