add gpg keypair create and export helper script
add gpg keypair create and export helper script

Add python helper script to create and export gpg keypairs.
It provides the option to set the gpg binary used to generate
the keys, the gpg homedir, hosts, email address and expiration
date as well as the option to delete the gpg homedir if it
already exists.

escapewindow/scriptworker,mozilla-releng/scriptworker,escapewindow/scriptworker,mozilla-releng/scriptworker