Use test/format to verify database file portability

After pursuing the option of using Python test suite to verify database file cross-endian portability in WT-4498, and encountered a huge number of "failures" (likely false positives we'd avoid putting effort to investigate), we plan to try a different option of using test/format to generate database files for portability verification. 

We have decided to go with using test/format is non-static, multi-threaded test that configures WiredTiger in a number of ways and performs random operations. The data files generated by test/format will also have good diversity coverage, by including different configuration options e.g. row, column, LSM, logging on/off, backup.