Avoid deleting ports assigned to router interfaces

Even though this method is marked to be removed, in
the meantime the fact that it's being agressive in
deleting all ports might mask underlying failures
with the remove_interface API call, so it's best to
relax it now to help catch potential gate failures.

Change-Id: I835942fb59ef8244f39fab59073e68c5bee3e44a
Close-bug: 1253848
Cleanup using about the data_utils module and functions again

HACKING officially discourages symbol import directly because it makes
it harder to track down that a function was imported. Recently, we keep
this rule and almost files were already fixed in
  Ibda1a5e424280bad8535ee27f66dec99bf68f676 .
But some files are not fixed. This commit cleanups them.

Change-Id: I92bf9097860738fbb79fad274b3e4cce07481f39
Merge "Avoid deleting ports assigned to router interfaces"
Merge "Cleanup using about the data_utils module and functions again"