Allow EXTRA_CLASSPATH to work on tar/source installations

Patch by brandonwillams, reviewed by David Capwell for CASSANDRA-15567

CHANGES.txt

@@ -1,5 +1,5 @@
 2.2.17
- * 
+ * Allow EXTRA_CLASSPATH to work on tar/source installations (CASSANDRA-15567)
 
 2.2.16
  * Fix SELECT JSON output for empty blobs (CASSANDRA-15435)

bin/cassandra

@@ -27,6 +27,7 @@
 # behavior, those variables are:
 #
 #   CLASSPATH -- A Java classpath containing everything necessary to run.
+#   EXTRA_CLASSPATH -- A Java classpath with anything to be appended to CLASSPATH
 #   JVM_OPTS -- Additional arguments to the JVM for heap size, etc
 #   JVM_ON_OUT_OF_MEMORY_ERROR_OPT -- The OnOutOfMemoryError JVM option if specified
 #   CASSANDRA_CONF -- Directory containing Cassandra configuration files.

bin/cassandra.in.sh

@@ -48,6 +48,9 @@ done
 for jsr223jar in "$CASSANDRA_HOME"/lib/jsr223/*/*.jar; do
     CLASSPATH="$CLASSPATH:$jsr223jar"
 done
+
+CLASSPATH="$CLASSPATH:$EXTRA_CLASSPATH"
+
 # JSR223/JRuby - set ruby lib directory
 if [ -d "$CASSANDRA_HOME"/lib/jsr223/jruby/ruby ] ; then
     export JVM_OPTS="$JVM_OPTS -Djruby.lib=$CASSANDRA_HOME/lib/jsr223/jruby"