Python 3.7: fix os.errno -> errno

In Python 3.7, there's no longer a os.errno, it's now available directly
from the root instead.

This patch therefore, tries to "import errno", and fallsback to
"import os.errno as errno" if it fails. Then in the content of the code,
we simply use the errno module directly.

Change-Id: Ibf385ab32a8098e936c019303633de38a848076c

ironic_inspector/pxe_filter/dnsmasq.py

@@ -20,6 +20,10 @@
 #     http://www.thekelleys.org.uk/dnsmasq/docs/dnsmasq-man.html
 
 
+try:
+    import errno
+except ImportError:
+    import os.errno as errno
 import fcntl
 import os
 import time
@@ -206,7 +210,7 @@ def _exclusive_write_or_pass(path, buf):
                 f.flush()
                 return True
             except IOError as e:
-                if e.errno == os.errno.EWOULDBLOCK:
+                if e.errno == errno.EWOULDBLOCK:
                     LOG.debug('%s locked; will try again (later)', path)
                     attempts -= 1
                     time.sleep(_EXCLUSIVE_WRITE_ATTEMPTS_DELAY)
@@ -261,7 +265,7 @@ def _configure_unknown_hosts():
         if os.stat(path).st_size == len(wildcard_filter):
             return
     except OSError as e:
-        if e.errno != os.errno.ENOENT:
+        if e.errno != errno.ENOENT:
             raise
 
     if _exclusive_write_or_pass(path, '%s' % wildcard_filter):

ironic_inspector/test/unit/test_dnsmasq_pxe_filter.py

@@ -11,6 +11,10 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+try:
+    import errno
+except ImportError:
+    import os.errno as errno
 import datetime
 import os
 
@@ -131,7 +135,7 @@ class TestExclusiveWriteOrPass(test_base.BaseTest):
 
     def test_write_would_block(self):
         err = IOError('Oops!')
-        err.errno = os.errno.EWOULDBLOCK
+        err.errno = errno.EWOULDBLOCK
         # lock/unlock paired calls
         self.mock_fcntl.side_effect = [
             # first try
@@ -156,7 +160,7 @@ class TestExclusiveWriteOrPass(test_base.BaseTest):
             'ironic_inspector.pxe_filter.dnsmasq._EXCLUSIVE_WRITE_ATTEMPTS',
             1))
         err = IOError('Oops!')
-        err.errno = os.errno.EWOULDBLOCK
+        err.errno = errno.EWOULDBLOCK
         self.mock_fcntl.side_effect = [err, None]
 
         wrote = dnsmasq._exclusive_write_or_pass(self.path, self.buf)
@@ -180,7 +184,7 @@ class TestExclusiveWriteOrPass(test_base.BaseTest):
     def test_write_custom_ioerror(self):
 
         err = IOError('Oops!')
-        err.errno = os.errno.EBADF
+        err.errno = errno.EBADF
         self.mock_fcntl.side_effect = [err, None]
 
         self.assertRaisesRegex(