Archive external redis log in external tests (#9765)

On test failure store the external redis server logs as CI artifacts so we can review them.

Write test name to server log for external server tests.
This is attempted and silently failed in case external server doesn't support it.
Note that in non-external server mode we use a more robust method of writing to the log which doesn't depend on the
server actually running/working. This isn't possible for externl servers and required for some complex tests which are
skipped in external mode anyway.

Cleanup: remove dup code.

.github/workflows/external.yml

@@ -15,12 +15,18 @@ jobs:
     - name: Build
       run: make REDIS_CFLAGS=-Werror
     - name: Start redis-server
-      run: ./src/redis-server --daemonize yes
+      run: ./src/redis-server --daemonize yes --logfile external-redis.log
     - name: Run external test
       run: |
           ./runtest \
             --host 127.0.0.1 --port 6379 \
             --tags -slow
+    - name: Archive redis log
+      if: ${{ failure() }}
+      uses: actions/upload-artifact@v2
+      with:
+        name: test-external-redis-log
+        path: external-redis.log
 
   test-external-cluster:
     runs-on: ubuntu-latest
@@ -30,7 +36,7 @@ jobs:
     - name: Build
       run: make REDIS_CFLAGS=-Werror
     - name: Start redis-server
-      run: ./src/redis-server --cluster-enabled yes --daemonize yes
+      run: ./src/redis-server --cluster-enabled yes --daemonize yes --logfile external-redis.log
     - name: Create a single node cluster
       run: ./src/redis-cli cluster addslots $(for slot in {0..16383}; do echo $slot; done); sleep 5
     - name: Run external test
@@ -39,4 +45,10 @@ jobs:
             --host 127.0.0.1 --port 6379 \
             --cluster-mode \
             --tags -slow
+    - name: Archive redis log
+      if: ${{ failure() }}
+      uses: actions/upload-artifact@v2
+      with:
+        name: test-external-cluster-log
+        path: external-redis.log