[test](cosmos-sdk) config cache size

[kien6034]

Problem definition
feature issue: #14

Changes made:
567f5aa

DefaultIAVLCacheSize       = 781_250
	IavlDisablefastNodeDefault = true

Tests that can check, when starting node, these value get set as the default config

[tnv1]

Currently, we can not access iavlCacheSize and iavlDisableFastNode from store (because they're private fields and not exported public). So this test should be cover can get values same as default values when init app config