Unit test multi-writer app store

[Sriep]

• [x] I added unit tests for any code that added
• [ ] I updated the CHANGELOG.md
• [x] All IP is original and not copied from another source
• [x] I assign all copyright to Loom Network for the code in the pull request

Addresses https://github.com/loomnetwork/loomchain/issues/1342

[Sriep]

Warning running test with -race produces lots of errors, due to

					for _, data := range snapshot.Range(prefix) {
						temp = data.Key
						temp = data.Value
					}

which could potentally read data at the same time its being changed.