cqlsh return non-zero status when STDIN CQL fails

Patch By Jacob Becker a.k.a. plastikat; reviewed by Jordan West and Dinesh Joshi for CASSANDRA-15623

CHANGES.txt

@@ -1,4 +1,5 @@
 3.0.21
+ * cqlsh return non-zero status when STDIN CQL fails (CASSANDRA-15623)
  * Don't skip sstables in slice queries based only on local min/max/deletion timestamp (CASSANDRA-15690)
  * Memtable memory allocations may deadlock (CASSANDRA-15367)
  * Run evictFromMembership in GossipStage (CASSANDRA-15592)

bin/cqlsh.py

@@ -813,6 +813,10 @@ class Shell(cmd.Cmd):
         self.statement_error = False
         self.single_statement = single_statement
 
+    @property
+    def batch_mode(self):
+        return not self.tty
+
     @property
     def is_using_utf8(self):
         # utf8 encodings from https://docs.python.org/{2,3}/library/codecs.html
@@ -2681,8 +2685,8 @@ def main(options, hostname, port):
 
     shell.cmdloop()
     save_history()
-    batch_mode = options.file or options.execute
-    if batch_mode and shell.statement_error:
+
+    if shell.batch_mode and shell.statement_error:
         sys.exit(2)