Update to work with latest stevedore

stevedore no longer raises a KeyError when there's an entrypoint
missing. Instead we must supply a callback that handles that error.
Update inspection code to work with this.

Also bumps stevedore minimum to 1.16 ahead of the global-requirements
bot.

Closes-Bug: #1603542
Change-Id: I12af23f2525ac90e577bdd10bbfbbd9788e9551c
Depends-On: I8aa1ee52ff7de50488acb86e8920da89ddb05771

ironic_python_agent/inspector.py

@@ -42,13 +42,14 @@ _COLLECTOR_NS = 'ironic_python_agent.inspector.collectors'
 _NO_LOGGING_FIELDS = ('logs',)
 
 
+def _extension_manager_err_callback(names):
+    raise errors.InspectionError('Failed to load collector %s' % names)
+
+
 def extension_manager(names):
-    try:
-        return stevedore.NamedExtensionManager(_COLLECTOR_NS,
-                                               names=names,
-                                               name_order=True)
-    except KeyError as exc:
-        raise errors.InspectionError('Failed to load collector %s' % exc)
+    return stevedore.NamedExtensionManager(
+        _COLLECTOR_NS, names=names, name_order=True,
+        on_missing_entrypoints_callback=_extension_manager_err_callback)
 
 
 def inspect():

requirements.txt

@@ -19,6 +19,6 @@ pyudev # LGPLv2.1+
 requests>=2.10.0 # Apache-2.0
 rtslib-fb>=2.1.41 # Apache-2.0
 six>=1.9.0 # MIT
-stevedore>=1.10.0 # Apache-2.0
+stevedore>=1.16.0 # Apache-2.0
 WSME>=0.8 # MIT
 ironic-lib>=2.0.0 # Apache-2.0