The 16.10 release of the neutron-openvswitch charm changed the
file management strategy of /etc/default/openvswitch-switch
config file from managing the file when dpdk is enabled to always
managing the file. Additionally, the template file was changed
in the 16.10 release to modify the file header (commit 4463c334).
These two changes guarantee that the contents of the file will
change when upgrading the charm.
The changing file contents causes the openvswitch-switch service
to be restarted, which in turn causes a data plane outage. This
commit fixes that by migrating the /etc/default/openvswitch-switch
to be charm managed without restarting the openvswitch-switch
service.
The change will only attempt to migrate versions of the file
which were created before 16.10 by searching for a marker in the
rendered version of the file which was added in 16.10.
Change-Id: Icc0f326991be239b88a57292740473f501181ebb
Closes-Bug: #1712444
e3ec31c91d