Harden analyzedb further against dropped/recreated tables (#10669)

Commit 445fc7cc hardened some parts of analyzedb. However, it missed a
couple of cases.

1) When the statement to get the modcount from the pg_aoseg table failed
due to a dropped table, the transaction was also terminated. This caused
further modcount queries to fail and while those tables were analyzed,
it would error and not properly record the mod count. Therefore, we now
restart the transaction when it errors.

2) If the table is dropped and then recreated while analyzedb is running
(or some other mechanism that results in the table being successfully
analyzed, but the pg_aoseg table did not exist during the initial
check), the logic to update the modcount may fail. Now, we skip the
update for the table if this occurs. In this case, the modcount would
not be recorded and the next analyzedb run will consider the table
modified (or dirty) and re-analyze it, which is the desired behavior.

gpMgmt/bin/analyzedb

@@ -210,9 +210,13 @@ def get_partition_state_tuples(pg_port, dbname, catalog_schema, partition_info):
                 modcount = dbconn.querySingleton(conn, modcount_sql)
             except pg.DatabaseError as e:
                 if "does not exist" in str(e):
-                    logger.debug("Table %s.%s (%s) no longer exists", schemaname, partition_name, tupletable)
+                    logger.info("Table %s.%s (%s) no longer exists and will not be analyzed", schemaname, partition_name, tupletable)
                 else:
                     logger.error(str(e))
+                if conn:
+                    conn.close()
+                # If there's an exception, the transaction is closed so we need to reconnect
+                conn = dbconn.connect(dburl)
             else:
                 num_sqls += 1
                 if num_sqls == 1000: # The choice of batch size was chosen arbitrarily
@@ -683,8 +687,9 @@ class AnalyzeDb(Operation):
         for schema_table in (x for x in self.success_list if
                              x not in heap_partitions and x not in root_partition_col_dict):
             # update modcount for tables that are successfully analyzed
-            new_modcount = curr_ao_state_dict[schema_table]
-            prev_ao_state_dict[schema_table] = new_modcount
+            if schema_table in curr_ao_state_dict:
+                new_modcount = curr_ao_state_dict[schema_table]
+                prev_ao_state_dict[schema_table] = new_modcount
 
             # update last op for tables that are successfully analyzed
             last_op_info = curr_last_op_dict[schema_table]  # {'CREATE':'<entry>', 'ALTER':'<entry>', ...}