Don't shuffle next tags

[ajoaoff]

When getting the next available tag, remove the shuffling of the available tags.
To avoid race conditions, add a lock to the method.
The lock is unique in the Link class, avoiding possible deadlocks.

[viniarck]

@ajoaoff nicely done. Looks good to me.

Very helpful for network operators as @italovalcy mentioned. Currently we have a rotating behavior as EVCs get deleted since available VLANs get appended, the rotating behavior also looks good to me:

kytos $> controller.switches['00:00:00:00:00:00:00:01'].interfaces[4].available_tags[:3]
Out[8]:
[TAG(<TAGType.VLAN: 1>, 4),
 TAG(<TAGType.VLAN: 1>, 5),
 TAG(<TAGType.VLAN: 1>, 6)]

kytos $> controller.switches['00:00:00:00:00:00:00:01'].interfaces[4].available_tags[-3:]
Out[9]:
[TAG(<TAGType.VLAN: 1>, 4094),
 TAG(<TAGType.VLAN: 1>, 4095),
 TAG(<TAGType.VLAN: 1>, 1)]

Before you merge this PR, could you run the e2e tests to make sure it's all set? Recently we also got an error on this test case test_085_create_and_remove_ten_circuit_concurrently kytos-ng/kytos-end-to-end-tests#182, and that one exercises core points of this change.

[ajoaoff]

I've run the end to end tests with success, merging the PR.