install_cert.yml

Now you can install the same service credentials for multiple services
(preferably not on the same host, that's still gonna result in at least
one service using the wrong certificate). This might be legitimate for
dependent services that need some of the float functionality (like x509)
without being actually modeled at the services.yml level. An example
would be replds@acme.

Also fix the x509_csr module to no longer depend on magic 'float'
variables but accept instead its parameters as arguments. And fix
the Docker templates to account for multiple credentials with different
names.