LU-8207 scripts: add auto-stripe option to lfs_migrate

LU-8207 scripts: add auto-stripe option to lfs_migrate

Add a "-A" flag to lfs_migrate, which will automatically select the
stripe count as the file is rewritten. Initial algorithm to
determine stripe count is sqrt(size_in_GB)+1, with an additional cap
on object size, though the algorithm or thresholds could conceivably
change in the future.  The primary intent for this feature is to be
able to give users a tool to fix stripe settings on existing files
based on file size.

A new "-C" flag specifies the object size cap.  On each OST, the
amount of space available for migration is capped by dividing the
free space of the smallest OST by the specified value.

A new "-M" flag allows OSTs with free space less than the specified
value to be considered unavailable for migration.

A new "-v" flag increases verbosity to help debug what is being done.

A new "-X" flag limits the amount of free space on each OST that
can be used for migration to the specified value.  This flag is
useful for testing by simulating OSTs that are nearly full.

A new sanity test verifies the operation of the new "-A" flag.

Lustre-change: https://review.whamcloud.com/20552
Lustre-commit: 99d7a8ed43be126b2769ad8bb0b5350cd328ed7f

Test-Parameters: trivial
Signed-off-by: Nathan Dauchy <nathan.dauchy@nasa.gov>
Signed-off-by: Steve Guminski <stephenx.guminski@intel.com>
Change-Id: I9ce8b64e028d9abb66b6b49cf7675263fd7202f0
Signed-off-by: Nathaniel Clark <nclark@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/36958
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>