Fix error on vlan reservation and add backward compatibility to Port.label_range

[italovalcy]

Fix #200

Heads-UP: this PR depends on atlanticwave-sdx/datamodel#141

Description of the change

• VLAN reservation routine had a bug where if the user requests a VLAN which is not on the VLAN table (meaning: the OXP does not specify that VLAN on their allowed range -- which by the way should be discussed), the TEManager._reserve_vlan call would fail with KeyError when running unit test:

FAILED tests/test_te_manager.py::TEManagerTests::test_connection_amlight_to_zaoxi_user_port_v2 - KeyError: 777

• Added backward compatibility to Port.label_range (also handled on datamodel PortHandler)

[coveralls]

Pull Request Test Coverage Report for Build 10350365886

Details

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.7%) to 85.956%

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Totals
Change from base Build 10271724419:	0.7%
Covered Lines:	1108
Relevant Lines:	1267

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💛 - Coveralls