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>

testutil/loopback_linux.go

@@ -21,6 +21,8 @@ func NewLoopback(size int64) (string, func() error, error) {
 	}
 
 	if err := file.Truncate(size); err != nil {
+		file.Close()
+		os.Remove(file.Name())
 		return "", nil, errors.Wrap(err, "failed to resize temp file")
 	}
 	file.Close()
@@ -29,6 +31,7 @@ func NewLoopback(size int64) (string, func() error, error) {
 	losetup := exec.Command("losetup", "--find", "--show", file.Name())
 	p, err := losetup.Output()
 	if err != nil {
+		os.Remove(file.Name())
 		return "", nil, errors.Wrap(err, "loopback setup failed")
 	}