Honor /HTTP_PROXY/i environment variable if set when executing babushka bootstrap script
Use default POSIX shell when executing babushka bootstrap script

Signed-off-by: Laurent Vallar <val@zbla.net>
Merge pull request #5 from Val/honor_http_proxy_and_use_default_posix_shell_on_babushka_bootstrap

Honor http proxy and use default posix shell on babushka bootstrap