The `nomad tls cert` command did not create certificates with the correct SANs for
them to work with non default domain and region names. This changset updates the
code to support non default domains and regions in the certificates.
Not setting the host name led the Go HTTP client to expect a certificate
with a DNS-resolvable name. Since Nomad uses `${role}.${region}.nomad`
names ephemeral dir migrations were broken when TLS was enabled.
Added an e2e test to ensure this doesn't break again as it's very
difficult to test and the TLS configuration is very easy to get wrong.
