Make linux build of OpenSSL deterministic

OpenSSL was embedding a timestamp causing its build to be non-deterministic.
Change deps-linux to be deterministic by using FAKETIME as needed and disabling it when it gets in the way.

Built five times (w/ LXC) and got the same output every time:

    a535e8c3fc6a34b9f35d82cba66164bf909378059fbeee8e383836499ff5bd69  bitcoin-deps-linux32-gitian-r3.zip
    b393572305abfafad81d76b8d73053b381adafe9042585344106c6fa6d285545  bitcoin-deps-linux64-gitian-r3.zip

This will make the Linux build output deterministic.