[V3] Rename get_region to show_region

[GET /resources] methods should be "list_<resource name>s"
or "show_<resource name>", so this patch applies the rule
to region client

Partially implements blueprint consistent-service-method-names

Change-Id: I5fc446b2e5f8931a1a8b27b0db03956a0e3ad8b2
3 files changed