qemu_cpu.cfg: introduce rhel_major_version variant name

This way we can make filters that include/exclude all RHEL-6 versions.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

qemu/tests/cfg/qemu_cpu.cfg

@@ -16,12 +16,14 @@
     variants qemu_flavor:
         - @unknown:
         - rhel:
-            variants rhel_version:
-                - 6_0:
-                - 6_1:
-                - 6_2:
-                - 6_3:
-                - 6_4:
+            variants rhel_major_version:
+                - 6:
+                    variants rhel_version:
+                        - 6_0:
+                        - 6_1:
+                        - 6_2:
+                        - 6_3:
+                        - 6_4:
         - upstream:
             variants qemu_version:
                 - 1_0:
@@ -33,8 +35,8 @@
 
     # uncomment the line corresponding to the QEMU version, if you know it:
     only (qemu_flavor = unknown)
-    #only (qemu_flavor = rhel).(rhel_version = 6_4)
-    #only (qemu_flavor = upstream).(qemu_version = 1_5)
+    #only (qemu_flavor = rhel)..(rhel_version = 6_4)
+    #only (qemu_flavor = upstream)..(qemu_version = 1_5)
 
     # CPU model lists:
     variants: