After updating pylint, it started emitting additional "E"
warnings in some cases, fix them.
unsubscriptable-object,
unsupported-delete-operation
These were associated with the OVN AgentCache code. Instead
of using a subscript, create get/delete methods to do the
same thing.
used-before-assignment
Re-factor some code so it's clear to pylint variables are
being assigned properly.
Trivialfix
Change-Id: I4a5ccb7f33465705e59b5274c41db3c371862b1e
126d54badc