Add default for `node_shared_openssl`.
Add default for `node_shared_openssl`.

It's not defined in 0.6 and earlier, and the behavior in those versions
is to always build with shared OpenSSL.

davedoesdev/ursa,quartzjer/ursa,darrenmce/ursa,IbpTeam/node-ursa,darrenmce/ursa,joyent/ursa,davedoesdev/ursa,joyent/ursa,mansona/ursa,IbpTeam/node-ursa,quartzjer/ursa,darrenmce/ursa,mansona/ursa,mansona/ursa,davedoesdev/ursa,joyent/ursa,darrenmce/ursa,quartzjer/ursa,IbpTeam/node-ursa,mansona/ursa,joyent/ursa,IbpTeam/node-ursa