rgw: mark ec related rgw suites as slow backend

We want to avoid tests that time out due to a too slow backend.

Reviwed-by: Josh Durgin <josh.durgin@inktank.com>
Signed-off-by: Yehuda Sadeh <yehuda@redhat.com>
(cherry picked from commit 85221bc325)

rgw_pool_type/ec-cache.yaml

@@ -2,3 +2,5 @@ overrides:
   rgw:
     ec-data-pool: true
     cache-pools: true
+  s3tests:
+    slow_backend: true

rgw_pool_type/ec-profile.yaml

@@ -6,3 +6,5 @@ overrides:
       k: 3
       m: 1
       ruleset-failure-domain: osd
+  s3tests:
+    slow_backend: true

rgw_pool_type/ec.yaml

@@ -1,3 +1,5 @@
 overrides:
   rgw:
     ec-data-pool: true
+  s3tests:
+    slow_backend: true