Fix snapcraft review-tools warning

```
Error while processing...
Processing...|
The store was unable to accept this snap.
  - package contains external symlinks:
    usr/lib/jvm/java-11-openjdk-amd64/lib/security/blacklisted.certs ->
    /etc/java-11-openjdk/security/blacklisted.certs
```

Our snap pakge is probably not good, this fix is probably
a workaround.

see:
* https://forum.snapcraft.io/t/resolve-package-contains-external-symlinks-error-when-trying-to-snap/2963
* https://bugs.openjdk.org/browse/JDK-8253866