Support separate privsep logging levels

Currently we don't have os_brick DEBUG log levels in Nova when setting
the service to debug mode.

That happens because Nova is forcefully setting oslo.privsep.daemon
levels to INFO to prevent leaking instance XML details (bug #1784062).

Oslo Privsep now supports per-context debug log levels, so this patch
sets the log level name for its only os_brick privsep context to
"os_brick.privileged" to differentiate it from the service it runs under
which uses the default "oslo_privsep.daemon".

This way even though Nova is still disabling its own privileged calls it
won't affect os-brick privileged calls, allowing us to properly debug
block device attach/detach operations.

Closes-Bug: #1922052
Related-Bug: #1784062
Change-Id: I0de32021eb90ca045845a6c7c7e3d27e52895948
(cherry picked from commit a82b2ffce5ad11b591130df40500b2fb1673a129)
(cherry picked from commit 30ddb1761045dfc551e0b218b375842a14c42b0e)

os_brick/privileged/__init__.py

@@ -31,4 +31,5 @@ default = priv_context.PrivContext(
     cfg_section='privsep_osbrick',
     pypath=__name__ + '.default',
     capabilities=capabilities,
+    logger_name=__name__,
 )

releasenotes/notes/privsep-logs-9e938e5a2aee042e.yaml

@@ -0,0 +1,11 @@
+---
+features:
+  - |
+    Support separate privsep logging levels. Now services using os-brick can
+    have different log levels for the service and os-brick's privsep calls.
+    The service usually uses the default "oslo_privsep.daemon" name while
+    os-brick now uses "os_brick.privileged".
+fixes:
+  - |
+    `Bug #1922052 <https://bugs.launchpad.net/nova/+bug/1922052>`_: Fixed
+    missing os-brick DEBUG logs on nova compute service.