Windows slave: support the master returning HTTPS URL

Since we update the front-end to answer with HTTPS url, that
the GCE slave cannot use, we need to alos accept HTTPS urls.

Change-Id: I1319da6047bc2c2bbeda8a9bfb6db54d3a8dd0c0
diff --git a/gce/jenkins-slave-windows.ps1 b/gce/jenkins-slave-windows.ps1
index 80714e9..e26d214 100644
--- a/gce/jenkins-slave-windows.ps1
+++ b/gce/jenkins-slave-windows.ps1
@@ -114,8 +114,8 @@
 # Replace the host name in the JNLP file, because Jenkins, in its infinite
 # wisdom, does not let us change that separately from its external hostname.
 $jnlp=((New-Object Net.WebClient).DownloadString("http://${jenkins_master}/computer/${jenkins_node}/slave-agent.jnlp"))
-$jnlp=$jnlp -replace "http://ci.bazel.io", "http://${jenkins_master}"
-$jnlp=$jnlp -replace "http://ci-staging.bazel.io", "http://${jenkins_master}"
+$jnlp=$jnlp -replace "https?://ci.bazel.io", "http://${jenkins_master}"
+$jnlp=$jnlp -replace "https?://ci-staging.bazel.io", "http://${jenkins_master}"
 Write-Output $jnlp | Out-File -Encoding ascii slave-agent.jnlp
 
 # Create the service that runs the Jenkins slave