tests: test_display_statistics: Reduce cache size

Since the test starts multiple caches, using the smaller size makes
it easier to run in virtualized testing environment with limited
cache device capacity.

Signed-off-by: Robert Baldyga <robert.baldyga@unvertical.com>

Author: robertbaldyga

test/functional/tests/stats/test_display_statistics.py

@@ -278,7 +278,7 @@ def test_core_nonconfig_stats(stat_filter):
 
 def storage_prepare():
     cache_dev = TestRun.disks["cache"]
-    cache_parts = [Size(20, Unit.GibiByte)] * caches_count
+    cache_parts = [Size(10, Unit.GibiByte)] * caches_count
     cache_dev.create_partitions(cache_parts)
     core_dev = TestRun.disks["core"]
     core_parts = [Size(10, Unit.GibiByte)] * cores_per_cache * caches_count