LU-14291 ofd: merge ost module into ofd

LU-14291 ofd: merge ost module into ofd

The ost module is very small and its very similar to the mds class
which is embedded in the mdt module. We can do the same thing with
the ost module. Merge it into the ofd module.

Test-Parameters: trivial
Change-Id: I1f7c44893d41ec8fc03113400a02b5076a07fbbe
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53993
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>