Bug 1764003

+++ This bug was initially created as a clone of Bug #1707731 +++

Description of problem:

Configuration handling was enhanced with patch https://review.gluster.org/#/c/glusterfs/+/18257/, Old configurations are not applied if Geo-rep session is created in the old version and upgraded.

Actual results:

All configurations reset when upgraded.


Expected results:

Configuration should be upgraded to the new format when Geo-replication is run for the first time after the upgrade.

--- Additional comment from Aravinda VK on 2019-05-17 06:53:49 UTC ---

## Reading Old format:

Config file consists of a section named "__section_order__", read that to get the order of different section. Sort the section based on order(based on values), and prepare a dict with values updated from each section.

For example:

```
[__section_order__]
sec1=0
sec2=2
sec3=1

[sec1]
log_level = INFO

[sec2]
log_level = DEBUG

[sec3]
log_level = ERROR
```

configs = {}
for sec in sorded_sections():
    for item_key, item_value in sec.items:
        configs[item_key] = item_value

With this logic, `log_level` will have final value "DEBUG"


## Upgrade:

During Geo-rep start(In gsyncd.py):

- Read the session config and see it is a new format or old
- If it is old format, read the config as explained above
- Compare the configs collected and write to new config only if it is different from Default configs
- Reload the new config

To get the old format config,

- Install old version of Glusterfs(<4) and create a geo-rep session.
- Set some configurations in Geo-rep
- Copy the config file for reference
- Old parsing code can be referred here https://github.com/gluster/glusterfs/blob/release-3.13/geo-replication/syncdaemon/configinterface.py