k3s download: increase `get_url` timeout 10→120s (#213)

The default `get_url` module timeout is 10s. As the k3s binary is around
60MB, it can take some time to download on slow connections or when many
downloads are concurrent (multi-node install).
Increase the timeout a bit from 10s to 120s.

Signed-off-by: Frank Villaro-Dixon <frank@villaro-dixon.eu>