env: Re-work environment code

* Instead of storing just a server_url which was necessary to
  regenerate the OpenVPN configs, instead store an env file.
* Move all the env parsing to `ovpn_genconfig` so that it can be re-run
  from genconfig instead of from `ovpn_init`.
* Remove all the parsing and env defaults except for genconfig.

NOTE: This breaks the older config method, uesrs will need to re-run
genconfig with an arg[1] as the previous server_url, this will create
the necessary env file the rest of the tools expect.

Example recovery for legacy users:

    host$ docker run --rm -it kylemanna/openvpn bash -l
    container# ovpn_genconfig $(cat /etc/openvpn/server_url)
genconfig: Add getopts parsing

* Pass public server URL via -u argument instead of $1
* Add ability to specify multiple alternative routes
* Add ability to specify override default server internal subnet
* Add ability to write configs without a default route out, not
  implemented in other configs yet
init: Rename to initpki

* This function only initialize the EasyRSA PKI tools now.
* Decoupled from the init process.
run: Handle NAT routes dynamically

* Handle the NAT routes dynamically
* Stop caring about backwards compatibility for now
genconfig: Handle route default env

* Handle re-inheriting previous routes if not overriden
* Handle leading whitespace