LU-10136 test: Lockahead test fixes

LU-10136 test: Lockahead test fixes

Two fixes:
1. Add version check for interop testing
2. Reduce count of locks requested in test15.  At 5000
locks, we would sometimes get some locks reclaimed during
the test due to memory pressure.  Reduce count to 500.

Signed-off-by: Patrick Farrell <paf@cray.com>
Change-Id: I693f8543b3579819aa64101ef30453627637ead6
Reviewed-on: https://review.whamcloud.com/29684
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Jenkins
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>