LU-14677 sec: no encryption key migrate/extend/resync/split

LU-14677 sec: no encryption key migrate/extend/resync/split

Allow some layout operations on encrypted files, even when the
encryption key is not available:
- lfs migrate
- lfs mirror extend
- lfs mirror resync
- lfs mirror verify
- lfs mirror split
We allow these access patterns to applications that know what they are
doing, by using the specific flag O_FILE_ENC and O_DIRECT.

Also add sanity-sec test_59a,b,c to exercise these access patterns.

Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Ieaeee0e5bf7643f18d775fe6daa5e31c2f349f8c
Reviewed-on: https://review.whamcloud.com/44024
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>