Make subvariant of armhfp appliances unique

When not specified, subvariant defaults to the variant. This leads to
both armhfp appliance and image_build based raw.xz image to have
identical metadata. A file with such issue can not be loaded by
productmd parser.

Due to another issue (that should be fixed in next Pungi release), the
paths to image directories are not listed in composeinfo.json file. The
compose-partial-copy script therefore has to find out if images should
be copied from the image metadata. And since there's an error in it, it
doesn't see the images and doesn't copy them.

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

fedora.conf

@@ -679,6 +679,7 @@ live_images = [
                 'repo': 'Everything',
                 'type': 'appliance',
                 'failable': True,
+                'subvariant': 'Workstation_Appliance',
                 }
     }),
     ('^Server$', {
@@ -687,6 +688,7 @@ live_images = [
                 'name': 'Fedora-Server-armhfp',
                 'type': 'appliance',
                 'failable': True,
+                'subvariant': 'Workstation_Appliance',
                 }
     }),
     ('^Spins$', {
@@ -719,7 +721,7 @@ live_images = [
                 'name': 'Fedora-Minimal-armhfp',
                 'repo': 'Everything',
                 'type': 'appliance',
-                'subvariant': 'Minimal',
+                'subvariant': 'Minimal_Appliance',
                 'failable': False,
                 },
                 {