This fixes issues in cvd download when network speed is slow.
Setting is passed to libcurl CURLOPT_TIMEOUT. Original default of 60s
was not enough if network speed is limited. Curl handles this as
total time for http(s) transfer.

https://curl.haxx.se/libcurl/c/CURLOPT_TIMEOUT.html

Also change commented out setting of ReceiveTimeout on example configs
to somewhat sensible value (1800s).

Signed-off-by: Tuomo Soini <tis@foobar.fi>