Enhanced CI cluster: now 3-node instead of 1-node

As it enables testing more sophisticated scenarios such as retries
and speculative executions, we made the cluster in CI consist
of 3 nodes. The existing tests pass seamlessly on such cluster.

.github/workflows/rust.yml

@@ -14,16 +14,12 @@ env:
 jobs:
   build:
     runs-on: ubuntu-latest
-    services:
-      scylladb:
-        image: scylladb/scylla
-        ports:
-          - 9042:9042
-        options: --health-cmd "cqlsh --debug" --health-interval 5s --health-retries 10
-        volumes:
-          - ${{ github.workspace }}:/workspace
     steps:
     - uses: actions/checkout@v2
+    - name: Setup 3-node Scylla cluster
+      run: |
+        sudo sh -c "echo 2097152 >> /proc/sys/fs/aio-max-nr"
+        GITHUB_WORKSPACE=${{ github.workspace }} docker-compose -f test/docker-compose.yml up -d
     - name: Format check
       run: cargo fmt --verbose --all -- --check
     - name: Clippy check
@@ -33,7 +29,9 @@ jobs:
     - name: Build
       run: cargo build --verbose --examples
     - name: Run tests
-      run: cargo test --verbose
+      run: SCYLLA_URI=172.42.0.2:9042 SCYLLA_URI2=172.42.0.3:9042 SCYLLA_URI3=172.42.0.4:9042 cargo test --verbose
+    - name: Stop cluster
+      run: GITHUB_WORKSPACE=${{ github.workspace }} docker-compose -f test/docker-compose.yml down
 
   # Tests that our current minimum supported rust version compiles everything sucessfully
   min_rust:

test/docker-compose.yml

@@ -0,0 +1,35 @@
+version: "3.7"
+
+networks:
+  public:
+    name: scylla_rust_driver_public
+    driver: bridge
+    ipam:
+      driver: default
+      config:
+        - subnet: 172.42.0.0/16
+services:
+  scylla1:
+    image: scylladb/scylla
+    volumes:
+      - ${GITHUB_WORKSPACE}:/workspace
+    networks:
+      public:
+        ipv4_address: 172.42.0.2
+    command: --rpc-address 172.42.0.2 --listen-address 172.42.0.2 --seeds 172.42.0.2 --skip-wait-for-gossip-to-settle 0
+  scylla2:
+    image: scylladb/scylla
+    volumes:
+      - ${GITHUB_WORKSPACE}:/workspace
+    networks:
+      public:
+        ipv4_address: 172.42.0.3
+    command: --rpc-address 172.42.0.3 --listen-address 172.42.0.3 --seeds 172.42.0.2 --skip-wait-for-gossip-to-settle 0
+  scylla3:
+    image: scylladb/scylla
+    volumes:
+      - ${GITHUB_WORKSPACE}:/workspace
+    networks:
+      public:
+        ipv4_address: 172.42.0.4
+    command: --rpc-address 172.42.0.4 --listen-address 172.42.0.4 --seeds 172.42.0.2,172.42.0.3 --skip-wait-for-gossip-to-settle 0