Cleanup loop devices after test failure

Cleans up loop devices if part of the test or mount process fails.

Also increases btrfs default file size to 650MB to accommodate
minimum btrfs size on ppc64le and s390x

Signed-off-by: Christopher Jones <tophj@linux.vnet.ibm.com>

fs/dtype_linux_test.go

@@ -20,16 +20,18 @@ func testSupportsDType(t *testing.T, expected bool, mkfs ...string) {
 	}
 	defer os.RemoveAll(mnt)
 
-	deviceName, cleanupDevice, err := testutil.NewLoopback(150 << 20) // 150 MB
+	deviceName, cleanupDevice, err := testutil.NewLoopback(100 << 20) // 100 MB
 	if err != nil {
 		t.Fatal(err)
 	}
 	if out, err := exec.Command(mkfs[0], append(mkfs[1:], deviceName)...).CombinedOutput(); err != nil {
 		// not fatal
+		cleanupDevice()
 		t.Skipf("could not mkfs (%v) %s: %v (out: %q)", mkfs, deviceName, err, string(out))
 	}
 	if out, err := exec.Command("mount", deviceName, mnt).CombinedOutput(); err != nil {
 		// not fatal
+		cleanupDevice()
 		t.Skipf("could not mount %s: %v (out: %q)", deviceName, err, string(out))
 	}
 	defer func() {