#3733: Improve vdt-update-certs (configuring location of CA certs)

vdt-update-certs needs two updates. Only the first is critical, and this
ticket can be resolved if the second isn't completed.

1) The location of the CA Certificates needs to be configurable. By this
I mean that it needs to be settable from the configuration file.
Currently it can be set from the command-line, but this is the wrong
method (it needs to persist in a file) and undocumented.

2) When running vdt-update-certs from the command-line, there is
absolutely no output. There should be some minimal output, unless
--quiet is passed. vdt-update-certs-wrapper should pass --quiet to
suppress the minimal output.