Use reader role for compute servers tests

Update all test files in tempest/api/compute/servers to use the reader
role for GET requests (list, show, get operations) following the pattern
in test_list_server_filters.py. This ensures proper RBAC testing by
using the project_reader credentials for read operations while
maintaining the primary credentials for write operations.

Additionally, remove redundant cls.client = cls.servers_client assignments
from individual test files and use cls.servers_client directly from the
base class instead. This eliminates redundant aliases and makes the code
more consistent.

Changes include:
- Added credentials = ['primary', 'project_reader'] to base class
- Set up reader_servers_client in base class setup_clients method
- Replaced all GET requests to use reader_servers_client instead of
  regular client
- Removed cls.client = cls.servers_client assignments from test files
- Replaced self.client with self.servers_client for write operations
- Replaced self.client with self.reader_servers_client for read
  operations where appropriate
- Updated files: test_availability_zone, test_server_group,
  test_server_addresses, test_server_tags, test_server_metadata,
  test_servers, test_instance_actions, test_attach_interfaces,
  test_disk_config, test_server_actions, test_server_personality,
  test_server_password, test_servers_negative, test_novnc,
  test_create_server, test_delete_server, test_list_server_filters,
  test_list_servers_negative, and related negative test files

Partial-Implements: blueprint test-nova-with-srbac-defaults
Change-Id: I4c5b35d7d1a8fa7155f2a31bc70116dfd681f948
Signed-off-by: Jason Paroly <jparoly@redhat.com>
27 files changed