distro: rename output of qcow2 image to disk.qcow2

Integration tests currently expect that and they need to be able to run
against lorax-composer (which outputs disk.qcow2) and osbuild-composer.

internal/distro/fedora30/distro.go

@@ -101,7 +101,7 @@ func New() *Fedora30 {
 	}
 
 	r.outputs["qcow2"] = output{
-		Name:     "image.qcow2",
+		Name:     "disk.qcow2",
 		MimeType: "application/x-qemu-disk",
 		Packages: []string{
 			"kernel-core",
@@ -122,7 +122,7 @@ func New() *Fedora30 {
 		},
 		KernelOptions: "ro biosdevname=0 net.ifnames=0",
 		IncludeFSTab:  true,
-		Assembler:     r.qemuAssembler("qcow2", "image.qcow2"),
+		Assembler:     r.qemuAssembler("qcow2", "disk.qcow2"),
 	}
 
 	r.outputs["openstack"] = output{

internal/distro/fedora30/distro_test.go

@@ -63,7 +63,7 @@ func TestFilenameFromType(t *testing.T) {
 		{
 			name:  "qcow2",
 			args:  args{"qcow2"},
-			want:  "image.qcow2",
+			want:  "disk.qcow2",
 			want1: "application/x-qemu-disk",
 		},
 		{

internal/distro/rhel82/distro.go

@@ -150,7 +150,7 @@ func New() *RHEL82 {
 	}
 
 	r.outputs["qcow2"] = output{
-		Name:     "image.qcow2",
+		Name:     "disk.qcow2",
 		MimeType: "application/x-qemu-disk",
 		Packages: []string{
 			"kernel-core",
@@ -170,7 +170,7 @@ func New() *RHEL82 {
 		},
 		IncludeFSTab:  true,
 		KernelOptions: "ro net.ifnames=0",
-		Assembler:     r.qemuAssembler("qcow2", "image.qcow2", 3*GigaByte),
+		Assembler:     r.qemuAssembler("qcow2", "disk.qcow2", 3*GigaByte),
 	}
 
 	r.outputs["openstack"] = output{

internal/distro/rhel82/distro_test.go

@@ -63,7 +63,7 @@ func TestFilenameFromType(t *testing.T) {
 		{
 			name:  "qcow2",
 			args:  args{"qcow2"},
-			want:  "image.qcow2",
+			want:  "disk.qcow2",
 			want1: "application/x-qemu-disk",
 		},
 		{