This is describing a real problem with your snap which is that the usr/lib/jvm/java-8-openjdk-armhf/jre/lib/security/cacerts file is pointing somewhere outside your snap, which is not guaranteed to exist. In this particular case, it will prevent ssl encrypted connections like https to not work within your snap.
This is described here (with workaround): https://bugs.launchpad.net/ubuntu/+source/snapcraft/+bug/1599281
I think if you install openjdk-8-jre-headless and ca-certificates-java on your system, then when you run snapcraft, snapcraft will pull them in. I’ve also had success using this in the snapcraft.yaml when using ‘snapcraft cleanbuild’:
UPDATE: added ‘openjdk-8-jre-headless’ to build-packages too since ca-certificates-java will pull in openjdk-9-jre-headless in cleanbuild.