snakemake: adapt env validation to fallback image

closes reanahub/reana-workflow-engine-snakemake#13

installation: bump shared modules

reana_client/validation/environments.py

@@ -13,7 +13,12 @@
 
 import requests
 
-from reana_commons.config import WORKFLOW_RUNTIME_USER_GID, WORKFLOW_RUNTIME_USER_UID
+from reana_commons.config import (
+    REANA_DEFAULT_SNAKEMAKE_ENV_IMAGE,
+    WORKFLOW_RUNTIME_USER_GID,
+    WORKFLOW_RUNTIME_USER_UID,
+)
+
 
 from reana_client.errors import EnvironmentValidationError
 from reana_client.config import (
@@ -476,5 +481,13 @@ def validate_environment(self):
         """Validate environments in REANA Snakemake workflow."""
         for step in self.workflow_steps:
             image = step["environment"]
+            if not image:
+                self.messages.append(
+                    {
+                        "type": "warning",
+                        "message": f"Environment image not specified, using {REANA_DEFAULT_SNAKEMAKE_ENV_IMAGE}.",
+                    }
+                )
+                image = REANA_DEFAULT_SNAKEMAKE_ENV_IMAGE
             kubernetes_uid = step.get("kubernetes_uid")
             self._validate_environment_image(image, kubernetes_uid=kubernetes_uid)

setup.py

@@ -42,7 +42,7 @@
     "cwltool==3.1.20210628163208",
     "jsonpointer>=2.0",
     "PyYAML>=5.1",
-    "reana-commons[yadage,snakemake]>=0.8.0a25,<0.9.0",
+    "reana-commons[yadage,snakemake]>=0.8.0a27,<0.9.0",
     "tablib>=0.12.1,<0.13",
     "werkzeug>=0.14.1",
 ]