`java`: import user certs to central cacerts store on prepare

[viceice]

We now have a central cacerts store fo all java versions.
As we need a jre to get the core cacerts file, we have the keytool available.

So we can now import all certs from /usr/local/share/ca-certificates/*.crt to the cert store on java prepare.

• Custom SSL certificate support #3
• [java] Create a central cacerts store #486