LU-4442 tests: update version number in replay-vbr test 7g

LU-4442 tests: update version number in replay-vbr test 7g

Since the following patch was landed on Lustre b2_5 branch,
we need change Lustre version number 2.5.52 to 2.5.1 in
replay-vbr test_7g():

Lustre-commit: 1eb9dbad0db49a4fb36d52f4141386b29baaedaf
Lustre-change: http://review.whamcloud.com/9213

Test-Parameters: envdefinitions=SLOW=yes,ONLY=7 testlist=replay-vbr
Test-Parameters: envdefinitions=SLOW=yes,ONLY=7 \
ossjob=lustre-b2_5 mdsjob=lustre-b2_5 \
ossbuildno=42 mdsbuildno=42 testlist=replay-vbr

Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: I28a4b2de285c92cc3d5934a77ef792e11fc897ed
Reviewed-on: http://review.whamcloud.com/9986
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Bob Glossman <bob.glossman@intel.com>
Reviewed-by: Emoly Liu <emoly.liu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>