Do not remove oracle jdk

Installing a package like libreoffice that requires java-1.8.0 will
install oracle jdk (jdk1.8). It seems to have a higher priority than
java-1.8.0-openjdk. So removing jdk1.8 will remove the package depending
on java.
We could force to install java-1.8.0-openjdk but it doesn't really makes
sense.
Installing jdk1.8 when an alternative is already set doesn't change
anything. So there should be no impact if it is installed.

JIRA INFRA-1405