Exclude specific backends from pruning (#262)

* Skip backends while pruning

* Add pruning test step and silence download log for better readability

* Add test cases for pruning in all backends

Also add -q or --quiet-pull to all tests.

* Add test case for skipping backends while pruning

* Adjusted test logging, generate new test spec file

* Gitignore for temp test file

test/zstd/run.sh

@@ -11,7 +11,7 @@ docker volume create app_data
 
 mkdir -p local
 
-docker run -d \
+docker run -d -q \
   --name offen \
   --network test_network \
   -v app_data:/var/opt/offen/ \
@@ -19,7 +19,7 @@ docker run -d \
 
 sleep 10
 
-docker run --rm \
+docker run --rm -q \
   --network test_network \
   -v app_data:/backup/app_data \
   -v ./local:/archive \