LU-5079 tests: decrease at_max value in replay-vbr test_7_cycle

LU-5079 tests: decrease at_max value in replay-vbr test_7_cycle

After commit 1d88909 (http://review.whamcloud.com/11213) was landed,
replay-vbr test 7* took long time to run due to more sleep time in
ptlrpc_set_wait(). This patch speeds up the tests by decreasing the
at_max value in test_7_cycle().

Test-Parameters: alwaysuploadlogs \
envdefinitions=SLOW=yes,ENABLE_QUOTA=yes \
mdtfilesystemtype=ldiskfs mdsfilesystemtype=ldiskfs ostfilesystemtype=ldiskfs \
clientdistro=el6 ossdistro=el6 mdsdistro=el6 \
mdtcount=1 mdssizegb=2 ostcount=7 ostsizegb=2 \
testlist=replay-vbr,replay-vbr

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: If24443955290b091fd22905dfb74b0d6a6d1b4e8
Reviewed-on: http://review.whamcloud.com/12490
Tested-by: Jenkins
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>