adding support for TLS

[sagar-sandbhor]

Script to test the changes required:

package main
import (
        "database/sql"
        "fmt"
        "os"
        _ "github.com/IBM/nzgo/v12"
)
func main() {
        host := "localhost"
        password := "password"
        securityLevel := "0"
        sslmode := "disable"        if(len(os.Args) >= 2){
            host = os.Args[1]
            password = os.Args[2]
            securityLevel = os.Args[3]
            sslmode = os.Args[4]
        }
        var connstring string =
                "user=admin " +
                "port=5480 " +
                "password=" + password + " " +
                "dbname=system " +
                "host="+ host + " " +
                "securityLevel=" + securityLevel + " " +
                "sslmode=" + sslmode + " " +
                "logLevel=info " +
                //"logPath= /tmp/ +
                "additionalLogFile=stdout"
				db, err := sql.Open("nzgo", connstring)
        if err != nil {
                fmt.Println(err)
                return
        }
        defer db.Close()
        rows, err := db.Query("select count(*) from _t_object")
        if err != nil {
                fmt.Println("Error: ", err)
                return
        }
        var count int
        for rows.Next() {
                _ = rows.Scan(&count)
                fmt.Println("object count : ", count)
        }
}

Output:

readHandshakeClientPacket ssl request=0
Attempting SSL_accept()
secure connection: protocol = TLSv1.2
SSL_accept succeeded with cipher = ECDHE-ECDSA-AES256-GCM-SHA384
connection: host=127.0.0.1 user=ADMIN database=SYSTEM remotepid=952420 fetype=12 conn=T
Session id is 17849