do not fail the sensor attribute when building an entity address

[nhoening]

Closes #456

Do warn about failure to build entity addresses, however.

This particular failure to build them has to do with the domain FlexMeasures runs on, which becomes part of the address.
When FlexMeasuresa starts, we don't know the domain ― currently, we find out where we run on request information.

Thus, warning about this failure in the terminal when FlexMeasures starts seems difficult. The failure becomes visual when the asset page is visited ("no entity address available"), so it will come up.

It will also come up if someone gets sensor data programmatically, via the API's GET /sensors endpoint, which also includes the entity address.

[coveralls]

Pull Request Test Coverage Report for Build 2632437510

• 5 of 8 (62.5%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.01%) to 68.367%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
flexmeasures/data/models/time_series.py	4	7	57.14%

Totals
Change from base Build 2611878330:	-0.01%
Covered Lines:	7095
Relevant Lines:	9843

---

💛 - Coveralls

[Flix6x]

Excellent. I also verified this resolves the issue when tunneling localhost.