Make OvsdbConnectionService instance-only
This patch ensures that the volatile data managed by
OvsdbConnectionService is stored per instance, and it removes the
static initialiser and all non-BluePrint instantiations. Other library
users can still create their own instances if necessary, but the
library code will no longer create multiple instances by default,
ensuring that BluePrint-mediated configuration changes are applied.
Change-Id: I41ca0c679d68e7dfeba3b5fd503194180358a9a2
JIRA: OVSDB-465
Signed-off-by: Stephen Kitt <skitt@redhat.com>