syscontainers: allow runtime defined in the configuration file

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

Closes: #1125
Approved by: TomSweeneyRedHat

Author: giuseppe

Atomic/syscontainers.py

@@ -154,6 +154,10 @@ def set_args(self, args):
         except (NameError, AttributeError):
             pass
 
+        if not self.user and not self.runtime:
+            self.runtime = self.get_atomic_config_item(["runtime"])
+
+
     @staticmethod
     def _split_set_args(setvalues):
         values = {}

docs/atomic-install.1.md

@@ -72,9 +72,11 @@ will only contain config and info files.
 
 **--runtime=PATH**
 Change the OCI runtime used by the systemd service file for running
-system containers and user containers.  The default **/bin/runc** is
-used for system containers.  Conversely, for user containers the
-default value is **/bin/bwrap-oci**.
+system containers and user containers.  If runtime is not defined, the
+value **runtime** in the configuration file is used for system
+containers.  If there is no runtime defined in the configuration file
+as well, then the default **/bin/runc** is used for system containers.
+Conversely, for user containers the default value is **/bin/bwrap-oci**.
 
 **--set=NAME=VALUE**
 Set a value that is going to be used by a system container for its