Support verbose logging in script `regen-test-files`.

Add support for option `-v`, `--verbose` to script
`test/utils/regen-test-files`. When enabled, set logging level to
`DEBUG` to log more information.

Also add some DEBUG-level logging statements for I/O operations
performed by the script.

Test: Run `test/utils/regen-test-files -m -v` and check that there are
      no changes among the generated files
Bug: 147814778
Bug: 152374989
Bug: 167385698
Bug: 182575630
Change-Id: Idac129aecc56b82ab96a3a22d6d7b9ade1870dfe
1 file changed