Use generic container.javaHome value

Make migration between different Java versions transparent

If the container.javaHome is not set the Docker instance won't start
raising the following error:

Cannot find a JRE or JDK. Please ensure that the JAVA_HOME environment
variable or container.javaHome in /var/gerrit/etc/gerrit.config is
set to a valid >=1.8 JRE location

Change-Id: Ibe518b0325098eef30ea81b5c2087941ee424f9a
diff --git a/gerrit/etc/gerrit.config.template b/gerrit/etc/gerrit.config.template
index 26fcb9f..630f1cb 100644
--- a/gerrit/etc/gerrit.config.template
+++ b/gerrit/etc/gerrit.config.template
@@ -41,7 +41,7 @@
 	javaOptions = "-Dflogger.backend_factory=com.google.common.flogger.backend.log4j.Log4jBackendFactory#getInstance"
 	javaOptions = "-Dflogger.logging_context=com.google.gerrit.server.logging.LoggingContext#getInstance"
 	user = gerrit
-	javaHome = /usr/lib/jvm/java-1.8.0-openjdk-1.8.0.242.b08-0.el7_7.x86_64/jre
+	javaHome = /usr/lib/jvm/jre
 	javaOptions = -Djava.security.egd=file:/dev/./urandom
 [receive]
 	enableSignedPush = false