Add support for quick disconnect to Disconnect-SsoAdminServer

In case one is connected just to one SSO server the cmdlet does not
need to take the -server parameter as it will be discovered from
$DefaultSsoAdminServers. In case there are more than 1 SSO servers
it will not disconnect any connection, instead it will ask to be more
precise using the Server parameter.

Modules/VMware.vSphere.SsoAdmin/VMware.vSphere.SsoAdmin.psm1

@@ -170,15 +170,42 @@ function Disconnect-SsoAdminServer {
    [CmdletBinding()]
    param(
       [Parameter(
-      Mandatory=$true,
          ValueFromPipeline = $true,
          ValueFromPipelineByPropertyName = $false,
          HelpMessage = 'SsoAdminServer object')]
       [ValidateNotNull()]
       [VMware.vSphere.SsoAdminClient.DataTypes.SsoAdminServer]
-   $Server)
+      $Server
+   )
 
    Process {
+      if (-not $PSBoundParameters['Server']) {
+         switch (@($global:DefaultSsoAdminServers).count) {
+            { $_ -eq 1 } { $server = ($global:DefaultSsoAdminServers).ToArray()[0] ; break }
+            { $_ -gt 1 } { 
+               $PSCmdlet.ThrowTerminatingError(
+                  [System.Management.Automation.ErrorRecord]::new(
+                     ([System.ApplicationException]"Connected to more than 1 SSO server, please specify a SSO server via -Server parameter"),
+                     'Disconnect-SsoAdminServer.ConnectedToMoreThanOneSSO',
+                     [System.Management.Automation.ErrorCategory]::InvalidOperation,
+                     $global:DefaultSsoAdminServers
+                  )
+               )
+               break 
+            }
+            Default { 
+               $PSCmdlet.ThrowTerminatingError(
+                  [System.Management.Automation.ErrorRecord]::new(
+                     ([System.ApplicationException]"Not connected to SSO server."),
+                     'Disconnect-SsoAdminServer.NotConnectedToSSO',
+                     [System.Management.Automation.ErrorCategory]::ConnectionError,
+                     $global:DefaultSsoAdminServers
+                  )
+               )
+             }
+         } 
+      }
+
       if ($global:DefaultSsoAdminServers.Contains($Server)) {
          $global:DefaultSsoAdminServers.Remove($Server) | Out-Null
       }