samples: big_http_download: Allow to configure number of iterations

Initially, this was intended to be a sample for manual "burnout"
testing, e.g. see if a device with it can run for 24hrs, or download
1GB of data, or similar.

It's however also useful for automated CI testing, but then we need
to have more specific completion criteria. So, allow to specify
number of download iterations via local Kconfig.

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
2 files changed