Add lager dependency
Add logging instrumentation to bksw_io

This begins integration of lager and logging instrumentation for
bookshelf. The bksw_io module has been instrumented with error logging
and debug logging.

lager is currently disabled for error_logger handler redirect to keep
logs visible in common test reports.
Add debug logging for bks_sec
Set the stage for multi-version disk format upgrades

After completing the 0 -> 1 migration, we revisit the
upgrade_disk_format function with a fresh call to
disk_format_version(). This way we validate that the migration is
recognized and set ourselves up to be able to support 0 -> 3 upgrade
via 0 -> 1 -> 2 -> 3