Enable to create legacy router

Some deployments create by default HA routers, this change enables to
force the creation of a legacy router using:

 openstack router create --no-ha ...

Closes-Bug: #1675514
Change-Id: I78f7dc3640a2acfdaf085e0e387b30373e8415f1

doc/source/command-objects/router.rst

@@ -64,7 +64,7 @@ Create new router
         [--project <project> [--project-domain <project-domain>]]
         [--enable | --disable]
         [--distributed]
-        [--ha]
+        [--ha | --no-ha]
         [--description <description>]
         [--availability-zone-hint <availability-zone>]
         <name>
@@ -94,6 +94,10 @@ Create new router
 
     Create a highly available router
 
+.. option:: --no-ha
+
+    Create a legacy router
+
 .. option:: --description <description>
 
     Set router description