Use 1804-style deprovisioning for all versions >= 18.04 (#1483)

18.04 changed the method of managing resolv.conf vs. 16.04; the new method involves letting systemd-networkd manage that file. A previous fix corrected waagent behavior for 18.04 but did not do so for subsequent releases. Now that Ubuntu's direction is clear, this commit makes the correction in all versions of Ubuntu from 18.04 onwards. Other distros are unaffected by this bug and by this fix.

azurelinuxagent/pa/deprovision/factory.py

@@ -34,7 +34,7 @@ def get_deprovision_handler(distro_name=DISTRO_NAME,
     if distro_name == "arch":
         return ArchDeprovisionHandler()
     if distro_name == "ubuntu":
-        if Version(distro_version) in [Version('18.04')]:
+        if Version(distro_version) >= Version('18.04'):
             return Ubuntu1804DeprovisionHandler()
         else:
             return UbuntuDeprovisionHandler()