Fix the message of coverage directory error

If a coverage-report directory conflicts, the error message is
incomplete like the following:

$ nova coverage-start --combine
Coverage collection started
$
$ nova coverage-report --html test01
Report path: /tmp/nova-coverage_Krl__k/test01
$
$ nova coverage-start --combine
Coverage collection started
$ nova coverage-report --html test01
ERROR: Directory conflict: %s already exists (HTTP 400)
$

This patch fixes the message.

Fixes bug #1217315

Change-Id: Ie21b0e87262a3caef36d93711ee96529ec699cec

nova/api/openstack/compute/contrib/coverage_ext.py

@@ -215,7 +215,7 @@ class CoverageController(object):
                 coverInst.xml_report(outfile=path)
             elif html:
                 if os.path.isdir(path):
-                    msg = _("Directory conflict: %s already exists")
+                    msg = _("Directory conflict: %s already exists") % path
                     raise exc.HTTPBadRequest(explanation=msg)
                 coverInst.html_report(directory=path)
             else:

nova/api/openstack/compute/plugins/v3/coverage.py

@@ -248,7 +248,7 @@ class CoverageController(wsgi.Controller):
                 coverInst.xml_report(outfile=path)
             elif html:
                 if os.path.isdir(path):
-                    msg = _("Directory conflict: %s already exists")
+                    msg = _("Directory conflict: %s already exists") % path
                     raise exc.HTTPBadRequest(explanation=msg)
                 coverInst.html_report(directory=path)
             else: