Modify link failure handler to leverage topology update messages

[italovalcy]

Fix #161

Heads-Up: this PR depends on https://github.com/atlanticwave-sdx/pce/pull/206

Description of the change

• Upon receiving a topology update message, get the failed links from PCE
• adding fixes to the existing link failure handler
• enhance the connections per link map mainly in two aspects: 1) consider inter-domain links (which are the most important aspect for link failure handler, once intra-OXP the OXPO is likely to handle the failure); 2) removing connections was not removing from the map correctly
• adding logging messages to help network operator troubleshoot eventual future issues

[coveralls]

Pull Request Test Coverage Report for Build 10351028132

Details

• 19 of 28 (67.86%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.9%) to 53.513%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
sdx_controller/handlers/lc_message_handler.py	0	3	0.0%
sdx_controller/handlers/connection_handler.py	18	24	75.0%
<!--	Total:	19	28	67.86%	-->

Totals
Change from base Build 10152046668:	0.9%
Covered Lines:	789
Relevant Lines:	1505

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💛 - Coveralls