This add support for Azure snitch. The work is an adaptation of
AzureSnitch for Apache Cassandra by Yoshua Wakeham:
https://raw.githubusercontent.com/yoshw/cassandra/9387-trunk/src/java/org/apache/cassandra/locator/AzureSnitch.java
Also change `production_snitch_base` to protect against
a snitch implementation setting DC and rack to an empty string,
which Lubos' says can happen on Azure.
Fixes#8593Closes#9084
* github.com:scylladb/scylla:
scylla_util: Use AzureSnitch on Azure
production_snitch_base: Fallback for empty DC or rack strings
azure_snitch: Azure snitch support