[Training 3.0] Add interlock file to data directories

[dslik]

In order to avoid situations where the wrong data directory is used, or when an old data directory is used, we should write an "interlock" file into the data directory that indicates the following information:

• The version of the MLPerf tools used to create the data
• The type of data stored in the data directory

When a data directory is used, the MLPerf tool should check the interlock file to make sure that the versions match up, and that the right type of data is present. If not, an error message should be displayed indicating the problem.