LU-827 tests: fix user ID for sanityn test_60

LU-827 tests: fix user ID for sanityn test_60

If sanityn.sh test_60() is run on a test system before any of the
quota users are configured, the test will fail.  The test does not
require that any specific user ID is used, so instead use RUNAS_ID
(which is a numeric value and does not even need to be defined in
/etc/passwd for this test to work).

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: Iaca88344e0dc615f44417e4175e5cddd146c2a7a
Reviewed-on: http://review.whamcloud.com/3021
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Reviewed-by: Yu Jian <yujian@whamcloud.com>