bitbake: codeparser/data_smart: Optimise parsing speed

bitbake: codeparser/data_smart: Optimise parsing speed

The previous "contains" changes caused a ~3% parsing speed impact.
Looking at the cause of those changes was interesting:

* Use of defaultdict was slower than just checking for missing entries
  and setting them when needed.
* Even the "import collections" adversely affects parsing speed
* There was a missing intern function for the contains cache data
* Setting up a log object for each variable has noticeable overhead
  due to the changes in the code paths uses, we can avoid this.
* We can call getVarFlag on "_content" directly within VariableParse
  for a noticeable speed gain since its a seriously hot code path.

This patch therefore tweaks the code based on the above observations to
get some of the speed back.

(Bitbake rev: fca802187a2a30686a8a07d2b6b16a3e5716e293)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>