ldb: ldbdump key and pack format version comments

ldb: ldbdump key and pack format version comments

For testing we need to know the actual KV level key of records and each
record's pack format version. This patch makes ldbdump add comments with
that info. We will parse it out in python tests.

Signed-off-by: Aaron Haslett <aaronhaslett@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>
Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Wed May 22 05:58:17 UTC 2019 on sn-devel-184