在RobotFramework--RIDE中把日期转化为整型进行运算
运行结果：
20180906 16:10:17.919 : INFO : ${time} = 2018-09-06 16:10:17
20180906 16:10:17.924 : INFO : ${time_2} = 2018-09-06 16:08:17
20180906 16:10:17.927 : INFO : ${time_2} = 2018-09-07 16:10:17
20180906 16:10:17.930 : INFO : ${number} = 201809061610
20180906 16:10:17.932 : INFO : ${number_2} = 201809061612
20180906 16:10:17.933 : INFO : ${number_3} = 201809061613
20180906 16:10:17.936 : INFO : ${number_4} = 201809061614