[ci] Use bitcoindevkit/electrs base image for electrum tests

.github/workflows/cont_integration.yml

@@ -78,8 +78,12 @@ jobs:
   test-electrum:
     name: Test Electrum
     runs-on: ubuntu-16.04
+    container: bitcoindevkit/electrs
     env:
-      MAGICAL_RPC_COOKIEFILE: /home/runner/.bitcoin/regtest/.cookie
+      MAGICAL_RPC_AUTH: USER_PASS
+      MAGICAL_RPC_USER: admin
+      MAGICAL_RPC_PASS: passw
+      MAGICAL_RPC_URL: 127.0.0.1:18443
       MAGICAL_ELECTRUM_URL: tcp://127.0.0.1:60401
     steps:
       - name: checkout
@@ -99,7 +103,7 @@ jobs:
           toolchain: stable
           override: true
       - name: start core
-        run: ./ci/start-core.sh || exit 1
+        run: ./ci/start-core.sh
       - name: test
         uses: actions-rs/cargo@v1
         with: