[plugin][ovn-central] timeout on non-leader host

[IMPACT]
When running the ovn_central plugin on a non-leader host the sbctl command hangs indefinitely until the sosreport timeout kicks in.

[TEST CASE]
* Run 'sos report -a' (AKA sosreport -a) which should exercise ovn-central, if the detection criteria are met. In this case if package 'ovn-central' is installed.

AND/OR

* Run 'sos report -o ovn_central' (AKA sosreport -o ovn_central) which will enable the ovn_central plugin only.

* The plugin will then timeout and logs will be as follows:

Setting up plugins ...
[plugin:ovn_central] Could not open DB schema file /usr/share/openvswitch/ovn-nb.ovsschema: [Errno 2] No such file or directory: '/usr/share/openvswitch/ovn-nb.ovsschema'
[plugin:ovn_central] Could not open DB schema file /usr/share/openvswitch/ovn-sb.ovsschema: [Errno 2] No such file or directory: '/usr/share/openvswitch/ovn-sb.ovsschema'
[plugin:ovn_central] added cmd output 'ovn-nbctl show'
[plugin:ovn_central] added cmd output 'ovn-sbctl show'
[plugin:ovn_central] added cmd output 'ovn-sbctl lflow-list'
[plugin:ovn_central] added cmd output 'ovn-nbctl get-ssl'
[plugin:ovn_central] added cmd output 'ovn-nbctl get-connection'
[plugin:ovn_central] added cmd output 'ovn-sbctl get-ssl'
[plugin:ovn_central] added cmd output 'ovn-sbctl get-connection'
[plugin:ovn_central] added cmd output 'ovn-nbctl list Load_Balancer'
[plugin:ovn_central] added cmd output 'ovn-nbctl list ACL'
[plugin:ovn_central] added cmd output 'ovn-nbctl list Logical_Switch_Port'
[plugin:ovn_central] added cmd output 'journalctl --no-pager --unit ovn-northd'
 Running plugins. Please wait ...

  Starting 1/1 ovn_central [Running: ovn_central]
[plugin:ovn_central] collecting path '/var/log/ovn/ovn-controller.log'
[plugin:ovn_central] collecting output of 'ovn-nbctl show'
[plugin:ovn_central] collecting output of 'ovn-sbctl show'

[WHERE PROBLEM COULD OCCUR]

If something arise after this change. It will only affect the data collection of the ovn-central plugin individually. It won't affect other plugins nor core functionalities.

Worse case scenario would be that user will have to collect ovn debugging data manually (outside a usual sosreport run) in order to provide it to a third-party support vendor.

[OTHER INFORMATION]

Upstream issue:
https://github.com/sosreport/sos/issues/2418

Upstream PR:
https://github.com/sosreport/sos/pull/2419