validate flat networks physical name

Modified flat driver to validate the physical network
name - we make sure that empty names are deducted.

unit test changes:
- added two tests to make sure that we detect empty
  physnet names
- fix bug in existing unit-tests
-- flat_networks should be a list of string and not string
- use conf to setup flat_network

Change-Id: Ib7cfbd3c97d2e95c82044a2cba683c917ea54a84
Partial-bug: #1325664
BSN: Remove db lock and add missing contexts

Adds context tracking decorators that were missing
from router interface methods. Without them, new
sessions were being created instead of using the
existing context which was causing transaction
issues.

Modifies the servermanager to store context references
as weakrefs so if multiple functions are called before
the rest functions are called, the first one doesn't steal
the only context reference with a pop() call.

Removes a DB lock for update in the server manager that occured
during rest calls that was triggering deadlocks due to the
file lock synchronization for the rest calls.

Closes-Bug: #1336251
Change-Id: Iad3d61e2c23832b3ad760a999fbab7feaa13f805
Merge "BSN: Remove db lock and add missing contexts"
Merge "validate flat networks physical name"