Linux installer does not recognize installed JDK11 instances

Issue Summary

When JDK 11 is installed, the Bitbucket installer still extracts and configures itself to use the bundled JRE.

Steps to Reproduce

1. Install JDK11 on server
2. Set environment variable for JAVA_HOME and JRE_HOME to point to the JDK installation
3. Run the Bitbucket Linux installer
   For Windows, see BSERV-11985

Expected Results

• The installed version of Java is found
• The bundled JRE is not extracted to the Bitbucket install directory
• The set-jre-home.sh is set to use what is set.

Actual Results

• The bundled JRE is extracted to the Bitbucket install directory
• The JRE_HOME is set to use the bundled JRE

Workaround

Modify $BITBUCKET_INSTALLATION/bin/set-jre-home.sh to explicitly point to your preferred JDK version:

if [ -z "$JRE_HOME" ]; then
    if [ -z "$JAVA_HOME" ]; then
        # If JRE_HOME and JAVA_HOME are not defined, edit this line to define JRE_HOME
        JRE_HOME="/usr/lib/jvm/java-11-oracle"

Notes

In JDK11 release notes, it notes that the JRE is no longer offered and only the JDK. This is evident in the structure difference:

JDK8

/usr/lib/jvm/java-8-oracle/jre/bin 

JDK11

/usr/lib/jvm/java-11-oracle/bin 

This too applies for openjdk.