openssl: do not build docs.

OpenSSL 1.0.1e doesn't build with Perl 5.18+ because of problems in
OpenSSL's pod files.  Since nobody is likely to look inside an
Omnibus package for OpenSSL documentation anyways, just avoid any
potential issues by skipping the docs when building OpenSSL.
Merge pull request #57 from sl4mmy/fix-openssl-docs-with-perl-5.18

openssl: fix documentation errors with perl 5.18.