Adding dry_run flag for salt.control state

Issue: on virtual environments where nested virtualization is not
       possible, we cannot get config drive iso files

Solution: generate config dirve isoes by running salt.control
          state with dry_run=True

As for comment in the code, I prefer to switch from start=True to
dry_run=False and switch to it.
This is why I added new flag. Product team can switch on the fly
and deprecate start=True usage

Prod-Related: PROD-29586

Change-Id: I2e5485e3e2a4fec06edc874de12fd50fb76d8264
diff --git a/_modules/virtng.py b/_modules/virtng.py
index 2da9d36..933d590 100644
--- a/_modules/virtng.py
+++ b/_modules/virtng.py
@@ -552,6 +552,7 @@
          nic='default',
          hypervisor=VIRT_DEFAULT_HYPER,
          start=True,  # pylint: disable=redefined-outer-name
+         dry_run=False,
          disk='default',
          saltenv='base',
          rng=None,
@@ -632,6 +633,8 @@
                     os.makedirs(img_dir)
 
                 if 'image' in args:
+                    if dry_run:
+                        continue
                     # Create disk from specified image
                     sfn = __salt__['cp.cache_file'](args['image'], saltenv)
                     try:
@@ -814,7 +817,7 @@
     xml = xml_doc.toxml()
     define_xml_str(xml)
 
-    if start:
+    if start and not dry_run:
         create(name)
 
     return True
diff --git a/salt/control/virt.sls b/salt/control/virt.sls
index 08e6158..187462c 100644
--- a/salt/control/virt.sls
+++ b/salt/control/virt.sls
@@ -62,6 +62,7 @@
   - mem: {{ size.ram }}
   - image: {{ node.image }}
   - start: True
+  - dry_run: False
   - disk: {{ size.disk_profile }}
   - nic: {{ size.net_profile }}
   {%- if node.rng is defined %}