kata-env: Do not leave temp files on test

One of the test cases was not defer removing the tmpfile
it uses. Add that defer.

Signed-off-by: Graham Whaley <graham.whaley@intel.com>

cli/kata-env_test.go

@@ -762,6 +762,7 @@ func TestEnvShowSettingsInvalidFile(t *testing.T) {
 
 	tmpfile, err := ioutil.TempFile("", "envShowSettings-")
 	assert.NoError(t, err)
+	defer os.Remove(tmpfile.Name())
 
 	// close the file
 	tmpfile.Close()