Prompt for user/password in deploy_stack.ps1
Prompt for user/password in deploy_stack.ps1

This commit updates the Windows deploy_stack.ps1 to set the
basic-auth-user and basic-auth-password secrets if absent.

Signed-off-by: John McCabe <a51dda7c7ff50b61eaea0444371f4a6a9301e501@johnmccabe.net>

rgee0/faas,alexellis/faas,rgee0/faas,alexellis/faas,rgee0/faas,alexellis/faas,openfaas/faas,rgee0/faas,rgee0/faas,alexellis/faas,alexellis/faas,alexellis/faas,rgee0/faas,openfaas/faas,rgee0/faas,rgee0/faas,openfaas/faas,alexellis/faas,alexellis/faas,rgee0/faas,rgee0/faas,alexellis/faas