#### 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.
**- Why I did it**
We were building a custom version of Supervisor because I had added patches to prevent hangs and crashes if the system clock ever rolled backward. Those changes were merged into the upstream Supervisor repo as of version 3.4.0 (http://supervisord.org/changes.html#id9), therefore, we should be able to simply install the vanilla package via pip. This will also allow us to easily move to Python 3, as Python 3 support was added in version 4.0.0.
**- How I did it**
- Remove Makefiles and patches for building supervisor package from source
- Install Python 3 supervisor package version 4.2.1 in Buster base container
- Also install Python 3 version of supervisord-dependent-startup in Buster base container
- Debian package installed binary in `/usr/bin/`, but pip package installs in `/usr/local/bin/`, so rather than update all absolute paths, I changed all references to simply call `supervisord` and let the system PATH find the executable to prevent future need for changes just in case we ever need to switch back to build a Debian package, then we won't need to modify these again.
- Install Python 2 supervisor package >= 3.4.0 in Stretch and Jessie base containers
libpython2.7, libdaemon0, libdbus-1-3, libjansson4 are common
across different containers. move them into docker-base-stretch
Signed-off-by: Guohan Lu <lguohan@gmail.com>
