Respect --insecure (-k) flag when fetching list_url. (#5178)
Respect --insecure (-k) flag when fetching list_url. (#5178)

* Respect --insecure when fetching list_url.
* Ensure support for Python 2.6, and that urlopen works for python versions prior 2.7.9 and between 3.0 and 3.4.3.

skosukhin/spack,iulian787/spack,mfherbst/spack,LLNL/spack,EmreAtes/spack,mfherbst/spack,matthiasdiener/spack,skosukhin/spack,EmreAtes/spack,lgarren/spack,iulian787/spack,TheTimmy/spack,mfherbst/spack,iulian787/spack,LLNL/spack,TheTimmy/spack,iulian787/spack,skosukhin/spack,EmreAtes/spack,krafczyk/spack,LLNL/spack,matthiasdiener/spack,iulian787/spack,skosukhin/spack,TheTimmy/spack,matthiasdiener/spack,matthiasdiener/spack,krafczyk/spack,EmreAtes/spack,lgarren/spack,LLNL/spack,tmerrick1/spack,TheTimmy/spack,LLNL/spack,mfherbst/spack,skosukhin/spack,mfherbst/spack,krafczyk/spack,lgarren/spack,matthiasdiener/spack,tmerrick1/spack,lgarren/spack,EmreAtes/spack,tmerrick1/spack,tmerrick1/spack,krafczyk/spack,lgarren/spack,krafczyk/spack,tmerrick1/spack,TheTimmy/spack