updates to linux host command to only attempt to resolve IPV4 A Records

[stevematyas]

As of 5.8.0 (https://github.com/iontorrent/TS/commit/a3d0246b7ca84ddb68700642a50a89a20c036888), the TS build process requires several external dependencies be downloaded.

During the TS build process, several error messages are reported such as: Could not find a valid ION_UPDATE_SERVER. and then later when attempting to download the src URL omits any hostname (thus src='http:///...' instead of src='http://<ION_UPDATE_SERVER>/...':

e.g. console log

[  2%] [  4%] -- downloading...
     src='http:///updates/software/external/cuda-linux64-16.04-rel-8.0.44-21122537.tar.gz'
     dst='/src/build/gpu/../cuda_toolkit-8.0.44-21122537-prefix/src/cuda-linux64-16.04-rel-8.0.44-21122537.tar.gz'
     timeout='3600 seconds'

Steps To Reproduce:

$ cd ~
$ git clone git@github.com:iontorrent/TS.git
$ cd TS
$ docker pull iontorrent/tsbuild
$ docker run -v $(pwd):/src iontorrent/tsbuild &> docker-build.log.txt

[stevematyas]

thanks @ipan