Remove a Link in the network as part of a Maintenance (i.e. Link decommission)

[ajoaoff]

Original issue opened by @italovalcy at kytos#19.

Description: when the network operator needs to decommission a Link, the orchestration tool should follow a sequence of steps to ensure no service will be affected

Expected deliverables:

• Support the procedure described below:

The following procedure should be followed to decommission a link:
a) move EVCs from the source link (the one being decommissioned) to a new destination link (what about EVC with the static path? What about non-EVCs?) (which services are we talking about: EVCs or Flow entries? Only EVCs)
- be careful with possible conflicts on the VLAN id used in source and destination link.
==> We need to discuss the role of MEF_ELINE Napp: is it supposed to do all the provisioning and maintenance/resilience of a link? Maybe we can have something like: mef_eline provisioning and mef_eline resilience (and mef_eline be only a meta package)
b) change the backup path of existing EVCs not to include this link under decommissioning
c) disable services which cannot be migrated
d) disable the interfaces