Adds an acceptance test to the ARM Availability Set to show that tagging

and updating of tags work as expected

Also updated the documentation for azure rm availability set to
demonstrate this

builtin/providers/azurerm/resource_arm_availability_set_test.go

@@ -32,6 +32,40 @@ func TestAccAzureRMAvailabilitySet_basic(t *testing.T) {
 	})
 }
 
+func TestAccAzureRMAvailabilitySet_withTags(t *testing.T) {
+
+	resource.Test(t, resource.TestCase{
+		PreCheck:     func() { testAccPreCheck(t) },
+		Providers:    testAccProviders,
+		CheckDestroy: testCheckAzureRMAvailabilitySetDestroy,
+		Steps: []resource.TestStep{
+			resource.TestStep{
+				Config: testAccAzureRMVAvailabilitySet_withTags,
+				Check: resource.ComposeTestCheckFunc(
+					testCheckAzureRMAvailabilitySetExists("azurerm_availability_set.test"),
+					resource.TestCheckResourceAttr(
+						"azurerm_availability_set.test", "tags.#", "2"),
+					resource.TestCheckResourceAttr(
+						"azurerm_availability_set.test", "tags.environment", "Production"),
+					resource.TestCheckResourceAttr(
+						"azurerm_availability_set.test", "tags.cost_center", "MSFT"),
+				),
+			},
+
+			resource.TestStep{
+				Config: testAccAzureRMVAvailabilitySet_withUpdatedTags,
+				Check: resource.ComposeTestCheckFunc(
+					testCheckAzureRMAvailabilitySetExists("azurerm_availability_set.test"),
+					resource.TestCheckResourceAttr(
+						"azurerm_availability_set.test", "tags.#", "1"),
+					resource.TestCheckResourceAttr(
+						"azurerm_availability_set.test", "tags.environment", "staging"),
+				),
+			},
+		},
+	})
+}
+
 func TestAccAzureRMAvailabilitySet_withDomainCounts(t *testing.T) {
 
 	resource.Test(t, resource.TestCase{
@@ -121,6 +155,39 @@ resource "azurerm_availability_set" "test" {
 }
 `
 
+var testAccAzureRMVAvailabilitySet_withTags = `
+resource "azurerm_resource_group" "test" {
+    name = "acceptanceTestResourceGroup1"
+    location = "West US"
+}
+resource "azurerm_availability_set" "test" {
+    name = "acceptanceTestAvailabilitySet1"
+    location = "West US"
+    resource_group_name = "${azurerm_resource_group.test.name}"
+
+    tags {
+	environment = "Production"
+	cost_center = "MSFT"
+    }
+}
+`
+
+var testAccAzureRMVAvailabilitySet_withUpdatedTags = `
+resource "azurerm_resource_group" "test" {
+    name = "acceptanceTestResourceGroup1"
+    location = "West US"
+}
+resource "azurerm_availability_set" "test" {
+    name = "acceptanceTestAvailabilitySet1"
+    location = "West US"
+    resource_group_name = "${azurerm_resource_group.test.name}"
+
+    tags {
+	environment = "staging"
+    }
+}
+`
+
 var testAccAzureRMVAvailabilitySet_withDomainCounts = `
 resource "azurerm_resource_group" "test" {
     name = "acceptanceTestResourceGroup1"

website/source/docs/providers/azurerm/r/availability_set.html.markdown

@@ -22,6 +22,10 @@ resource "azurerm_availability_set" "test" {
     name = "acceptanceTestAvailabilitySet1"
     location = "West US"
     resource_group_name = "${azurerm_resource_group.test.name}"
+    
+    tags {
+        environment = "Production"
+    }
 }
 ```
 
@@ -40,6 +44,7 @@ The following arguments are supported:
 * `platform_update_domain_count` - (Optional) Specifies the number of update domains that are used. Defaults to 5.
 
 * `platform_fault_domain_count` - (Optional) Specifies the number of fault domains that are used. Defaults to 3.
+* `tags` - (Optional) A mapping of tags to assign to the resource. 
 
 ## Attributes Reference