provide the possibility to use one copy of the directory "easy-rsa" to generate various keys in various paths

In new plase user must only 
copy openssl<version>.cnf from ${EASY_RSA}
setup this file so how it should be
run `. ${EASY_RSA}/vars`
and then run ${EASY_RSA}/clean-all
...
for example, if EASY_RSA is /usr/share/easy-rsa, and work dir /etc/openvpn/server

cd /etc/openvpn/server
cp -a /usr/share/easy-rsa/openssl-<ver>.cnf ./
. /usr/share/easy-rsa/vars
/usr/share/easy-rsa/clean-all
# same as in documentation

line
export PWD=`pwd`
possible not need