test/rocksdb: only use 2GB cache for per-patch testing

We can still use 4GB for nightly testing, but cutting
the cache size to 2GB reduces the setup time for each
of the 5 db_bench test runs.

Signed-off-by: Jim Harris <james.r.harris@intel.com>
Change-Id: Ic946cfcd2ecac209e0e06b05777c18ccdec50d14

Reviewed-on: https://review.gerrithub.io/436564
Chandler-Test-Pool: SPDK Automated Test System <sys_sgsw@intel.com>
Reviewed-by: Shuhei Matsumoto <shuhei.matsumoto.xt@hitachi.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>

test/blobfs/rocksdb/rocksdb.sh

@@ -55,11 +55,12 @@ timing_exit mkfs
 
 mkdir $output_dir/rocksdb
 RESULTS_DIR=$output_dir/rocksdb
-CACHE_SIZE=4096
 if [ $RUN_NIGHTLY -eq 1 ]; then
+	CACHE_SIZE=4096
 	DURATION=60
 	NUM_KEYS=100000000
 else
+	CACHE_SIZE=2048
 	DURATION=20
 	NUM_KEYS=20000000
 fi