bugfix: Fix duplicate 'address' in standlone SRIOV

bugfix: Fix duplicate 'address' in standlone SRIOV

* Add unit test per Rodolfo's comment

Creating a VM using generted xml file /tmp/vm_sriov_0.xml returns
an XML error: missing source address type.

This fix modifies generted xml from:
<source>
<address>
<address bus="0x1a" domain="0x0000" function="0x0" slot="0x10" type="pci" />
</address>
</source>

to:

<source>
<address bus="0x1a" domain="0x0000" function="0x0" slot="0x10" type="pci" />
</source>

Change-Id: I694153e7468986bacb19ba3e09e761993aad7184
Signed-off-by: Dino Simeon Madarang <dinox.madarang@intel.com>
Reviewed-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>
Reviewed-by: Ross Brattain <ross.b.brattain@intel.com>
Reviewed-by: Alain Jebara <alain.jebara@intel.com>
Reviewed-by: Emma Foley <emma.l.foley@intel.com>