chore: restore and fix SSH tests on Windows Server Core images (#391)

While working on #388 I remembered we disabled SSH specific tests for Windows Server Core image in order to deliver a new image cf notes of #289.

This PR removes this skip and fix them by waiting 10s before trying to connect with SSH (5s wasn't enough), as discovered in #388 (comment).

tests/sshAgent.Tests.ps1

@@ -126,10 +126,11 @@ Describe "[$global:IMAGE_NAME] image has correct version of java and git-lfs ins
     }
 }
 
-Describe "[$global:IMAGE_NAME] create agent container with pubkey as argument" -Skip:($global:WINDOWSFLAVOR -eq 'windowsservercore') {
+Describe "[$global:IMAGE_NAME] create agent container with pubkey as argument" {
     BeforeAll {
         docker run --detach --tty --name="$global:CONTAINERNAME" --publish-all "$global:IMAGE_NAME" "$global:PUBLIC_SSH_KEY"
         Is-ContainerRunning $global:CONTAINERNAME | Should -BeTrue
+        Start-Sleep -Seconds 10
     }
 
     It 'runs commands via ssh' {
@@ -143,10 +144,11 @@ Describe "[$global:IMAGE_NAME] create agent container with pubkey as argument" -
     }
 }
 
-Describe "[$global:IMAGE_NAME] create agent container with pubkey as envvar" -Skip:($global:WINDOWSFLAVOR -eq 'windowsservercore') {
+Describe "[$global:IMAGE_NAME] create agent container with pubkey as envvar" {
     BeforeAll {
         docker run --detach --tty --name="$global:CONTAINERNAME" --publish-all --env="JENKINS_AGENT_SSH_PUBKEY=$global:PUBLIC_SSH_KEY" "$global:IMAGE_NAME"
         Is-ContainerRunning $global:CONTAINERNAME | Should -BeTrue
+        Start-Sleep -Seconds 10
     }
 
     It 'runs commands via ssh' {
@@ -162,11 +164,12 @@ Describe "[$global:IMAGE_NAME] create agent container with pubkey as envvar" -Sk
 
 
 $global:DOCKER_PLUGIN_DEFAULT_ARG="/usr/sbin/sshd -D -p 22"
-Describe "[$global:IMAGE_NAME] create agent container like docker-plugin with '$global:DOCKER_PLUGIN_DEFAULT_ARG' as argument" -Skip:($global:WINDOWSFLAVOR -eq 'windowsservercore') {
+Describe "[$global:IMAGE_NAME] create agent container like docker-plugin with '$global:DOCKER_PLUGIN_DEFAULT_ARG' as argument" {
     BeforeAll {
         [string]::IsNullOrWhiteSpace($global:DOCKER_PLUGIN_DEFAULT_ARG) | Should -BeFalse
         docker run --detach --tty --name="$global:CONTAINERNAME" --publish-all --env="JENKINS_AGENT_SSH_PUBKEY=$global:PUBLIC_SSH_KEY" "$global:IMAGE_NAME" "$global:DOCKER_PLUGIN_DEFAULT_ARG"
         Is-ContainerRunning $global:CONTAINERNAME | Should -BeTrue
+        Start-Sleep -Seconds 10
     }
 
     It 'runs commands via ssh' {