install.sh: check both openjdk-8 and openjdk-11
install.sh: check both openjdk-8 and openjdk-11

On Debian10, only Openjdk-11 is available, the install.sh fails in java
checking. Openjdk-8 and Openjdk-11 all work well, we should check both of them.
This patch also fixed the error message.

Signed-off-by: Amos Kong <eb01d8f828a6c9a20be4534e72e049aaf41503df@scylladb.com>

scylladb/scylla-jmx,scylladb/scylla-jmx,scylladb/scylla-jmx