DOWNLOAD_CONNECT_TIMEOUT changed from 10 to 30 because some file start only after 15 sec (see below).

Fetching boost_1_64_0.tar.bz2 from https://dl.bintray.com/boostorg/release/1.64.0/source/

% Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                               Dload  Upload   Total   Spent    Left  Speed
0     0    0     0    0     0      0      0 --:--:--  0:00:15 --:--:--     0

100 76.7M 100 76.7M 0 0 1863k 0 0:00:42 0:00:42 --:--:-- 8136k
/home/gitianuser/bitcoin/depends/work/download/boost-1_64_0/boost_1_64_0.tar.bz2.temp: OK

This is a backport of Core's PR14184