use Cleanup(),TempDir() in test cases (#5723)

Replace defer with t.Cleanup().

Replace the combination of ioutil.TempDir, error checking
and defer os.RemoveAll() with Go testing.T's new TempDir()
helper.

Mark auxiliary functions as test helpers.

.github/workflows/coverage.yml

@@ -44,7 +44,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v2
         with:
-          go-version: "^1.15.4"
+          go-version: "1.15"
       - uses: actions/checkout@v2
       - uses: technote-space/get-diff-action@v4
         with:
@@ -66,7 +66,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v2
         with:
-          go-version: "^1.15.4"
+          go-version: "1.15"
       - uses: actions/checkout@v2
       - uses: technote-space/get-diff-action@v4
         with:
@@ -78,6 +78,10 @@ jobs:
         with:
           name: "${{ github.sha }}-${{ matrix.part }}"
         if: env.GIT_DIFF
+      - name: Set up Go
+        uses: actions/setup-go@v2
+        with:
+          go-version: 1.15
       - name: test & coverage report creation
         run: |
           cat pkgs.txt.part.${{ matrix.part }} | xargs go test -mod=readonly -timeout 8m -race -coverprofile=${{ matrix.part }}profile.out -covermode=atomic

.github/workflows/docker.yml

@@ -16,7 +16,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v2
         with:
-          go-version: "^1.15.4"
+          go-version: "1.15"
       - uses: actions/checkout@master
       - name: Prepare
         id: prep

.github/workflows/e2e-nightly.yml

@@ -18,7 +18,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v2
         with:
-          go-version: '^1.15.4'
+          go-version: '1.15'
 
       - uses: actions/checkout@v2
 

.github/workflows/e2e.yml

@@ -15,7 +15,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v2
         with:
-          go-version: '^1.15.4'
+          go-version: '1.15'
       - uses: actions/checkout@v2
       - uses: technote-space/get-diff-action@v4
         with:

.github/workflows/release.yml

@@ -16,7 +16,7 @@ jobs:
 
       - uses: actions/setup-go@v2
         with:
-          go-version: '^1.15.4'
+          go-version: '1.15'
 
       - run: echo https://github.com/tendermint/tendermint/blob/${GITHUB_REF#refs/tags/}/CHANGELOG.md#${GITHUB_REF#refs/tags/} > ../release_notes.md 
 

.github/workflows/tests.yml

@@ -25,7 +25,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v2
         with:
-          go-version: "^1.15.4"
+          go-version: "1.15"
       - uses: actions/checkout@v2
       - uses: technote-space/get-diff-action@v4
         with:
@@ -57,7 +57,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v2
         with:
-          go-version: "^1.15.4"
+          go-version: "1.15"
       - uses: actions/checkout@v2
       - uses: technote-space/get-diff-action@v4
         with:
@@ -89,7 +89,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v2
         with:
-          go-version: "^1.15.4"
+          go-version: "1.15"
       - uses: actions/checkout@v2
       - uses: technote-space/get-diff-action@v4
         with:
@@ -120,7 +120,7 @@ jobs:
     steps:
       - uses: actions/setup-go@v2
         with:
-          go-version: "^1.15.4"
+          go-version: "1.15"
       - uses: actions/checkout@v2
       - uses: technote-space/get-diff-action@v4
         with: