Baremetal/utils should not log certain exceptions

unlink_without_raise was logging exceptions when it failed to unlink a
file, which is confusing since it is often called on non-existing files.

create_link_without_raise was also logging exceptions when it failed
to create a symlink.

This patch corrects this behaviour; both functions now explicitly check
for the type of error they expect, and then suppress that. If another
type of OSError is encountered, a warning is logged. This patch also
adds unit tests for both functions.

fixes bug 1097931.

Change-Id: Ie36f59dce34a6c67765770c5f968c003003acc88

nova/virt/baremetal/utils.py

@@ -15,6 +15,7 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+import errno
 import os
 
 from nova.openstack.common import log as logging
@@ -43,8 +44,11 @@ def inject_into_image(image, key, net, metadata, admin_password,
 def unlink_without_raise(path):
     try:
         os.unlink(path)
-    except OSError:
-        LOG.exception(_("Failed to unlink %s") % path)
+    except OSError, e:
+        if e.errno == errno.ENOENT:
+            return
+        else:
+            LOG.warn(_("Failed to unlink %(path)s, error: %(e)s") % locals())
 
 
 def write_to_file(path, contents):
@@ -55,9 +59,12 @@ def write_to_file(path, contents):
 def create_link_without_raise(source, link):
     try:
         os.symlink(source, link)
-    except OSError:
-        LOG.exception(_("Failed to create symlink from %(source)s to %(link)s")
-                % locals())
+    except OSError, e:
+        if e.errno == errno.EEXIST:
+            return
+        else:
+            LOG.warn(_("Failed to create symlink from %(source)s to %(link)s"
+                       ", error: %(e)s") % locals())
 
 
 def random_alnum(count):