#### Why I did it
The process of config generation (sonic-cfggen) fails, but the services continue to run with invalid config
#### How I did it
* add exit with error on errors in start.sh script (because supervisord relies on start.sh return code).
* fix jinja template. Jinja use common python expressions under the hood and `has_key` method was removed from dict in py3, so use check by `in` operator as it is supported by both py2 and py3.
#### How to verify it
* compile sonic with enabled iccp.
* add mclag config to CONFIG_DB.
```
'MC_LAG|1' => {
"local_ip": "10.0.0.2",
"peer_ip": "10.0.0.3",
"peer_link": "Ethernet8",
"mclag_interface": "Ethernet12"
}
* unmaks, enable and start swss and iccpd services in sonic.
* log in into the iccpd container and check the config file `/etc/iccpd/iccpd.conf`
* expected config:
```
mclag_id:1
local_ip:10.0.0.2
peer_ip:10.0.0.3
peer_link:Ethernet8
mclag_interface:Ethernet12
system_mac:YOUR_SYSTEM_MAC
#### Description for the changelog
Fixed initial iccpd startup configuration.
