This patch adds functionality Pegleg currently lacks: the ability to
regenerate expired certificates.
This patch adds:
1. CLI toggle --regenerate-all to generate_pki. Default is False,
which means if no certificates are present, generate what is in
the pki catalogue. If new certs have been added to the catalogue
generate just those. If the --regenerate-all flag is True, then
Pegleg will ignore any existing certs and regenerate (or generate
for the first time) all certificates defined in the PKI catalogue.
2. Documentation updates for CLI change.
3. Updates to pki_utility to accomodate the new flag.
4. Updates pki_generator methods to use rendered documents to
accommodate documents that have to be layered.
5. Updates pki_generator unit tests to include a layering definition
which is now required to run the commands.
Change-Id: I2d8086770e9226e44598ef40eca790981279f626