qga-win: Handle VSS_E_PROVIDER_ALREADY_REGISTERED error

This patch handles the case where VSS Provider is already registered,
where in such case qga uninstalls the provider and registers it again.

Signed-off-by: Sameeh Jubran <sjubran@redhat.com>
Signed-off-by: Basil Salman <basil@daynix.com>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

qga/vss-win32/install.cpp

@@ -443,6 +443,17 @@ STDAPI DllRegisterServer(void)
                                      VSS_PROV_SOFTWARE,
                                      const_cast<WCHAR*>(QGA_PROVIDER_VERSION),
                                      g_gProviderVersion);
+    if (hr == (long int) VSS_E_PROVIDER_ALREADY_REGISTERED) {
+        DllUnregisterServer();
+        hr = pVssAdmin->RegisterProvider(g_gProviderId, CLSID_QGAVSSProvider,
+                                         const_cast<WCHAR * >
+                                         (QGA_PROVIDER_LNAME),
+                                         VSS_PROV_SOFTWARE,
+                                         const_cast<WCHAR * >
+                                         (QGA_PROVIDER_VERSION),
+                                         g_gProviderVersion);
+    }
+
     if (FAILED(hr)) {
         errmsg_dialog(hr, "RegisterProvider failed");
     }