The following methods are now called from inside a reader context:
* ``VPNPluginDb.get_ipsec_site_connection``
* ``VPNPluginDb.get_ipsec_site_connections``
This avoids logged exceptions "ORM session: SQL execution without
transaction in progress"
Related-Bug: #2080072
Change-Id: I6555419c582b3c8654b13731d0b7c7fd61942957