fix getConsumerNameFromFileName to work with a longer file path

lib/parse_lag.js

@@ -14,12 +14,13 @@ function extract_header_fields(line) {
 // In order to easily resolve the consumer's name, we are using the filename as an identifier
 // Otherwise, you could use CLIENT_ID from the consumer lag report.
 // However, in our case, we attach a UUID and instance to every consumer making it very difficult to parse out the base consumer name.
-// Example: Expected input: "some_directory/consumerName~sometimestamp.txt"
+// Example: Expected input: "/opt/some_directory/consumerName~sometimestamp.txt"
 // Returns consumerName
 function getConsumerNameFromFileName(file_path) {
     let directory_and_file = file_path.split('~')[0];
-    // grab the second element, the filename to get the consumer's name
-    return directory_and_file.split('/')[1];
+    // grab the last element, the filename to get the consumer's name
+    let elements = directory_and_file.split('/');
+    return elements[elements.length-1];
 }
 
 // Parses a file. filename is assumed to contain the Consumer's name.