Parametrization of EASYRSA_CA_EXPIRE and EASYRSA_CERT_EXPIRE

[msarvinen]

I think it would add value for this project if CA and CERT expiration times could be modified when creating a server or a client. Currently script makes it by using 825 days. And at least in my case I want to use shorter times for a certain cases and longer times for another cases.

To be exact, I'm referring to these parameters:

In how many days should the root CA key expire?

#set_var EASYRSA_CA_EXPIRE 3650

In how many days should certificates expire?

#set_var EASYRSA_CERT_EXPIRE 825

Additional context
You have madea great script, makes world more secure and allows many admins to save lot of hours. Thank You!

[angristan]

Closing to centralize in #974