LBaaS: Fix incorrect pool status change

Avoid incorrect status change when deleting the pool.
We can check for the conditions prior putting the pool
to PENDING_DELETE state, in case delete conditions are met
it is safe to change the state to PENDING_DELETE.
Also, change create_vip and update_vip operations to respect
PENDING_DELETE and avoid race conditions.

Change-Id: I9f526901eb85bdb83cf4ff8131460eb592c900f8
Closes-Bug: #1242338
Fix error while creating l2 gateway services in nvp

Ensure that Conflict errors are not masked; also ensure
that coding errors do not mask NVP API errors.

Fixes bug #1244259

Change-Id: I27586d72af89fd39f6443dbab33f0e4e762b0c99
Merge "LBaaS: Fix incorrect pool status change"
Merge "Fix error while creating l2 gateway services in nvp"