Add option to ignore backend HTTP error in BigSwitch plugin

This patch fixes the way the BigSwitch plugin ignores 404
errors from the backend controller by allowing HTTP codes
to be selectively ignored on REST calls. This prevents
unnecessary exception handling and failover logic in calls
where 404 codes are acceptable.

Fixes: bug #1200023

(cherry picked from commit 5b4ef2a513bc7c8d2a2eecb57f656bf42bb0dd52)
Change-Id: Ia1118c039af3b45d96fb3f8a5fb5d3febdf50f4f