LU-12704 tests: component end must be multiple of stripesize

LU-12704 tests: component end must be multiple of stripesize

In racer file_create.sh, it was generating a random multiple of 64KB
in [64K..1024K] for the stripe_size, but using a fixed 1MB component
end.  However, the component end must be a multiple of stripe_size,
or an error will be returned by "lfs setstripe":

  Invalid layout: component end must be aligned by the stripe size

Generate the component_end argument as a random multiple [1..8] of
the stripe size for PFL, DoM, and FLR files.

Fixes: 0b66b11523cb ("LU-3285 tests: add dom into racer test suite")
Test-Parameters: trivial testlist=racer
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Ib79131fc71d0eaa4a398cd8c8adf6e53473ebbe5
Reviewed-on: https://review.whamcloud.com/36174
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: James Nunez <jnunez@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>