Update simulation tests

[fedekunze]

Ref: cosmos/cosmos-sdk#5378

Description

TODO:

• Remove dup code with SDK's SimApp
• Use SDK's master as target branch

---

For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer

---

For admin use:

• Added appropriate labels to PR (ex. WIP, R4R, docs, etc)
• Reviewers assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #215 into master will increase coverage by 2.58%.
The diff coverage is 92.5%.

@@            Coverage Diff             @@
##           master     #215      +/-   ##
==========================================
+ Coverage    66.4%   68.99%   +2.58%     
==========================================
  Files           5        4       -1     
  Lines         509      516       +7     
==========================================
+ Hits          338      356      +18     
+ Misses        140      129      -11     
  Partials       31       31

Impacted Files	Coverage Δ
app/app.go	89.61% <92.5%> (+0.72%)	⬆️

[alexanderbez]

ACK