use --release 7 instead of -source/-target

use --release 7 instead of -source/-target

Bug-Ubuntu: https://launchpad.net/bugs/1756854
Bug-Ubuntu: https://launchpad.net/bugs/1766998
Forwarded: no
Last-Update: 2018-04-24

Instead of -source/-target ceph should be build with --release for OpenJDK 9
or later so that the bootclasspath is also set, as per JEP-247, otherwise it
risks incurring into binary incompatibility when run with an earlier OpenJDK.
OpenJDK 11 minimum compatibility release has been updated to 7.
Last-Update: 2018-04-24
Gbp-Pq: Name update-java-source-target-flags.patch