Upstream changes change default cloud to nRF Cloud

[coderbyheart]

v1.2.15 introduced a new backend for nRF Connect for Cloud and made it the default backend.

The current release no longer work with AWS:

[00:00:00.732,513] <dbg> nrf_cloud_integration.cloud_wrap_init: ********************************************
[00:00:00.742,614] <dbg> nrf_cloud_integration.cloud_wrap_init:  The Asset Tracker v2 has started
[00:00:00.751,770] <dbg> nrf_cloud_integration.cloud_wrap_init:  Version:     1.2.16-thingy91_nrf9160ns-ltem-debug
[00:00:00.762,420] <dbg> nrf_cloud_integration.cloud_wrap_init:  Cloud:       nRF Cloud
[00:00:00.770,721] <dbg> nrf_cloud_integration.cloud_wrap_init:  Endpoint:    xxx-ats.iot.us-east-1.amazm
[00:00:00.782,226] <dbg> nrf_cloud_integration.cloud_wrap_init: ********************************************

[coderbyheart]

Closed via #38.
1.2.8 is the fixed release.