gitian: Make linux build of dependencies 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.

Outputs when built w/ KVM (and repeated with LXC), built a few times and they match every time:

Deps:

    05fe8e9aef00d295f24a94deef7d3a918af5aeef371ba57fdd5a6acd8c51f6cb  bitcoin-deps-linux32-gitian-r3.zip
    4227aa9d9fedbb4265b8d10a4f78b7435f34b00a54eb4d662bf78f59c6e70c27  bitcoin-deps-linux64-gitian-r3.zip

Boost:

    149a464f02aa809a340306d13fc0ecb1a347057ca99daf846100e7e3c53d85c2  boost-linux32-1.55.0-gitian-r1.zip
    c47bc1a5ffa5097c10280fb2fffb462a925cac5873c4ce7268e404281bddd133  boost-linux64-1.55.0-gitian-r1.zip

Result from building 0.9.0rc1 (15ec451) using the descriptors in this pull:

    20b208827262ad4a4afb2419e60bf27c16e96406e3df518f77d56771e22ab13f  bin/32/bitcoin-cli
    5d1f2a19bad40fb1c7f6ea0edaddf750820d8d1f5e17ab6071f88df8e174ca34  bin/32/bitcoin-qt
    260d5b0cdc10a7b7ea81f5cc51a8fe1533b3ca43e5470c78b830683e7d0ec354  bin/32/bitcoind
    557671b4ae41fb4561d83360e9da917a5b29a1c315fcf470d16230e4a5e64548  bin/32/test_bitcoin
    ab9b1078841c5d25cb9c05b3baf214e789b1640d5fab535c86191be4cccd0221  bin/32/test_bitcoin-qt
    20a93099050df6176afa3a5745b15e54be88831bd7deb91398038d6b57013917  bin/64/bitcoin-cli
    685784a29cd9d33b28c23cb1690e1bca4ae820c42c2f3a3dab8592236a10c050  bin/64/bitcoin-qt
    fafa628df8411c5b44bc770010ae577377d812548c10ef9e06f8b7f9a916b1e7  bin/64/bitcoind
    b62e830e6560fba96075964d406f9948b53fafd6c9009cd98caa1b87c4e87171  bin/64/test_bitcoin
    1427bba689501d22e16f2c380d7b45a247afbf84be222f692354eee4a7f5038e  bin/64/test_bitcoin-qt
    848875dca917077a5419e876e0ef234cd6b375a55904d08f8706d861eaa57f6b  bin/bitcoin-0.9.0.tar.gz