Don't allow rollback when we are enterprise enrolled.

As stated (and verified) by the device_policy protobuf, we can determine
whether a device is enterprise enrolled by checking if GetOwner is empty.
We use this knowledge to not allow rollback when powerwash is also requested (
the default).

As part of this CL I've figured out how to unittest Rollback and added tests
for both enterprise and non-enterprise rollback.

BUG=chromium:254829
TEST=Tested on both an enrolled and non-enrolled device. Verified only the
latter actually did a powerwash while the other aborted correctly. Also ran
new unittests

Change-Id: Idfe6bfef88819fe1bab7da6b31854faf7642c9ce
Reviewed-on: https://gerrit.chromium.org/gerrit/61645
Reviewed-by: David Zeuthen <zeuthen@chromium.org>
Commit-Queue: Chris Sosa <sosa@chromium.org>
Tested-by: Chris Sosa <sosa@chromium.org>

install_plan.h

diff --git a/install_plan.h b/install_plan.h
index b070cbe..c2f523e 100644
--- a/install_plan.h
+++ b/install_plan.h
@@ -99,7 +99,10 @@
     processor_->ActionComplete(this, kErrorCodeSuccess);
   }
 
-  virtual std::string Type() const { return "InstallPlanAction"; }
+  InstallPlan* install_plan() { return &install_plan_; }
+
+  static std::string StaticType() { return "InstallPlanAction"; }
+  virtual std::string Type() const { return StaticType(); }
 
   typedef ActionTraits<InstallPlanAction>::InputObjectType InputObjectType;
   typedef ActionTraits<InstallPlanAction>::OutputObjectType OutputObjectType;