remotectl: Add a new process tool

With an empty certificate command for now

Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>
common: Refactor the certificate loading/generation code

Put into its own file.

Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>
remotectl: Implement the remotectl certificate command

This creates a self-signed certificate if one is not available.
It prints out the path of the certificate that will be used.

Can specify the user and group that should own the certificate.

Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>
ws: Run cockpit-ws as non-root user and group

Add configure arguments to --with-cockpit-user=xxx which defaults
to root, and --with-cockpit-group=yyyy which defaults to no group
being explicitly set.

cockpit-ws is run as the cockpit-ws user/group. cockpit-session
is a setuid root program.

Closes #853
Reviewed-by: Patrick Uiterwijk <puiterwijk@redhat.com>
- Moved user and group generation in spec to %pre
- Use %attr to fix file ownership and permissions
Add remotectl to gitignore