LU-14286 tests: reduce fallocate space sanity 150e

LU-14286 tests: reduce fallocate space sanity 150e

Changes to fallocate have increase the time to allocate
space.  The increased run time is making sanity test
150e run long enough to time out.  We need to reduce the
amount of space santiy test 150e fallocates from 90%
to 100 MB per OST or 60% of available space if running
in SLOW mode to allow the test to complete.

Test-Parameters: trivial env=ONLY=150e fstype=ldiskfs testlist=sanity
Signed-off-by: James Nunez <jnunez@whamcloud.com>
Change-Id: Ic6ab41daf8f451c31d092849ccf6906747baa72d
Reviewed-on: https://review.whamcloud.com/41211
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>