LU-797 tests: speed up ost-pools tests

LU-797 tests: speed up ost-pools tests

The test time of the ost-pools subtests is unreasonably long.

test_14 fills an OST to 90% full, regardless of the OST size.
Skip the test if the amount of data to be written is too large
to run in a practical time.

test_18 creates 3x3x30000 files to compare performance with/without
pools enabled.  Instead of creating a fixed number of files, use
createmany to run for a specific (short) time to measure performance.

test_23 tried to fill all OSTs 100% full.  Split this test into two:
- test_23a to test quota with a file in a pool
- test_23b to test OOS with a file striped over pool

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ib851939a210ab68f52da1ac777781c2a922c500c
Reviewed-on: http://review.whamcloud.com/2028
Tested-by: Hudson
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>