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"