Upgrade load balanced API servers to v5.2

This step is for API servers in an HA environment, where there is a separate datanode that contains the database and RabbitMQ.

On the API servers, upgrade Abiquo to 5.2.x
```
yum update
```
Before you confirm, check the following packages will be installed from the abiquo-base repository:
1. jdk: 11.0.6u10
2. redis: 5.0.7.1

Check versions of Java and Tomcat

Click here to show/hide steps to check versions

Check that the symbolic link to the latest version of Java points to Java 11

# cd /usr/java
# ll
latest -> /usr/java/jdk-11.0.6+10

Check that the correct Tomcat version will be used

# cd /opt/abiquo/tomcat/bin
# sh version.sh
Using CATALINA_BASE:   /opt/abiquo/tomcat
Using CATALINA_HOME:   /opt/abiquo/tomcat
Using CATALINA_TMPDIR: /opt/abiquo/tomcat/temp
Using JRE_HOME:        /usr
Using CLASSPATH:       /opt/abiquo/tomcat/bin/bootstrap.jar:/opt/abiquo/tomcat/bin/tomcat-juli.jar
NOTE: Picked up JDK_JAVA_OPTIONS:  --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.io=ALL-UNNAMED --add-opens=java.rmi/sun.rmi.transport=ALL-UNNAMED
Server version: Apache Tomcat/9.0.33
Server built:   Mar 11 2020 09:31:38 UTC
Server number:  9.0.33.0
OS Name:        Linux
OS Version:     3.10.0-1160.15.2.el7.x86_64
Architecture:   amd64
JVM Version:    11.0.6+10
JVM Vendor:     AdoptOpenJDK

On the API Server in the JDK folder, check certificate migration for AM download. The API Server certificate should be listed for Java 11 with its FQDN. You may need to enter the storepass option to supply the password and you can use the alias option to search for the hostname or FQDN of your server

# cd /usr/java/jdk-11.0.6+10/lib/security
# keytool -list -keystore cacerts -alias (hostname or fqdn)

For example

sudo keytool -list -keystore cacerts -alias abiquo.example.com

On the API Servers, change file permissions so the Abiquo services can run as the tomcat user (not root) and allow access to the configuration files
```
chown -R tomcat /opt/abiquo
```