fix(memory leaks): MCOL-5791 - get rid of memory leaks in plugin code (#3365)

There were numerous memory leaks in plugin's code and associated code.
During typical run of MTR tests it leaked around 65 megabytes of
objects. As a result they may severely affect long-lived connections.

This patch fixes (almost) all leaks found in the plugin. The exceptions
are two leaks associated with SHOW CREATE TABLE columnstore_table and
getting information of columns of columnstore-handled table. These
should be fixed on the server side and work is on the way.

writeengine/bulk/we_bulkload.h

@@ -77,7 +77,7 @@ class BulkLoad : public FileOp
   /**
    * @brief Pre process jobs to validate and assign values to the job structure
    */
-  int preProcess(Job& job, int tableNo, TableInfo* tableInfo);
+  int preProcess(Job& job, int tableNo, std::shared_ptr<TableInfo>& tableInfo);
 
   /**
    * @brief Print job information
@@ -194,7 +194,7 @@ class BulkLoad : public FileOp
   std::string fAlternateImportDir;                 // Alternate bulk import directory
   std::string fErrorDir;                           // Opt. where error records record
   std::string fProcessName;                        // Application process name
-  static boost::ptr_vector<TableInfo> fTableInfo;  // Vector of Table information
+  static std::vector<std::shared_ptr<TableInfo>> fTableInfo;  // Vector of Table information
   int fNoOfParseThreads;                           // Number of parse threads
   int fNoOfReadThreads;                            // Number of read threads
   boost::thread_group fReadThreads;                // Read thread group