* fix(helm): add TLS params back

During a recent refactor, several TLS flags stopped being processed for
a few of the commands. This fixes those commands, and documents how to
set up TLS.

* fix(tiller): add stricter certificate verification

The older version of Tiller allowed a weaker set of certificate checks
than we intended. This version requires a client certificate, and then
requires that that certificate be signed by a known CA. This works
around the situation where a user could provide a self-signed
certificate.

Adds a testdata directory to hold tls certs at the root
of the project. The tests cover pkg/tlsutil, cmd/helm,
and cmd/helm/installer.

Closes #2289