Update public key cap to use powershell

plugins/guests/windows/cap/public_key.rb

@@ -37,7 +37,7 @@ module VagrantPlugins
 
           # Ensure the user's ssh directory exists
           remote_ssh_dir = "#{home_dir}\\.ssh"
-          comm.create_remote_directory(remote_ssh_dir)
+          comm.execute("New-Item -Path '#{remote_ssh_dir}' -ItemType directory -Force", shell: "powershell")
           remote_upload_path = "#{temp_dir}\\vagrant-insert-pubkey-#{Time.now.to_i}"
           remote_authkeys_path = "#{remote_ssh_dir}\\authorized_keys"
 
@@ -67,7 +67,7 @@ module VagrantPlugins
         # @return [Hash] {:temp, :home}
         def self.fetch_guest_paths(communicator)
           output = ""
-          communicator.execute("echo %TEMP%\necho %USERPROFILE%", shell: "cmd") do |type, data|
+          communicator.execute("Write-Output $env:TEMP\nWrite-Output $env:USERPROFILE", shell: "powershell") do |type, data|
             if type == :stdout
               output << data
             end

test/unit/plugins/guests/windows/cap/insert_public_key_test.rb

@@ -19,7 +19,7 @@ describe "VagrantPlugins::GuestWindows::Cap::InsertPublicKey" do
     allow(comm).to receive(:is_a?).and_return(true)
     allow(machine).to receive(:communicate).and_return(comm)
 
-    allow(comm).to receive(:execute).with(/echo .+/, shell: "cmd").and_yield(:stdout, "TEMP\r\nHOME\r\n")
+    allow(comm).to receive(:execute).with(/Write .+/, shell: "powershell").and_yield(:stdout, "TEMP\r\nHOME\r\n")
     allow(comm).to receive(:execute).with(/dir .+\.ssh/, shell: "cmd")
     allow(comm).to receive(:execute).with(/dir .+authorized_keys/, shell: "cmd", error_check: false).and_return(auth_keys_check_result)
     allow(comm).to receive(:create_remote_directory)
@@ -65,7 +65,7 @@ describe "VagrantPlugins::GuestWindows::Cap::InsertPublicKey" do
 
     context "when required directories cannot be fetched from the guest" do
       before do
-        expect(comm).to receive(:execute).with(/echo .+/, shell: "cmd").and_yield(:stdout, "TEMP\r\n")
+        expect(comm).to receive(:execute).with(/Write .+/, shell: "powershell").and_yield(:stdout, "TEMP\r\n")
       end
 
       it "should raise an error" do