Appveyor acs deployment upgrade mode (#411)

* Update azure-cloud-service.md

* Update environment-variables.md

appveyor/ci#1989

src/docs/deployment/azure-cloud-service.md

@@ -108,3 +108,7 @@ When deploying during the build session environment variables are used instead.
 ![project-environment-variables](/assets/img/docs/deployment/web-deploy/project-environment-variables.png)
 
 Variables defined during the build override those ones defined on Environment level.
+
+### Deployment Upgrade Mode
+
+AppVeyor exposes [DeploymentUpgradeMode Enumeration](https://msdn.microsoft.com/en-us/library/microsoft.windowsazure.management.compute.models.deploymentupgrademode.aspx) with "tweak" environment variable called `APPVEYOR_ACS_DEPLOYMENT_UPGRADE_MODE`. Default value is `Auto`. Set it to `Manual` or `Simultaneous` if different behavior is required.

src/docs/environment-variables.md

@@ -58,3 +58,4 @@ Environment variables that are set by AppVeyor for every build:
 * `APPVEYOR_BUILD_WORKER_IMAGE` - set build worker image for build to run on. Can be done only at build configuration level, not at build time
 * `APPVEYOR_SKIP_FINALIZE_ON_EXIT` - if `appveyor exit` or `Exit-AppVeyor` build was called, exit build even without **Finalize** steps (`on_success`, `on_finish` scripts and build cache save)
 * `APPVEYOR_SAVE_CACHE_ON_ERROR` - save build cache on build failure. By default build cache is being saved only during successful build **Finalize** steps
+* `APPVEYOR_ACS_DEPLOYMENT_UPGRADE_MODE`. Exposes [DeploymentUpgradeMode Enumeration](https://msdn.microsoft.com/en-us/library/microsoft.windowsazure.management.compute.models.deploymentupgrademode.aspx) when deploying Azure Cloud Service. Default value is `Auto`. Set it to `Manual` or `Simultaneous` if different behavior is required.