Confine errors from dnspython to dnsplug and use dkim errors, since dkim.__init__.py doesn't import dns and needs dkim errors (LP: #2018646)

dkim/__init__.py

@@ -802,7 +802,7 @@ class DomainSigner(object):
     except binascii.Error as e:
       self.logger.error('KeyFormatError: {0}'.format(e))
       return False
-    except dns.exception.Timeout as e:
+    except DnsTimeoutError as e:
       self.logger.error('DnsTimeoutError: Domain: {0} Selector: {1} Error message: {2}'.format(
           sig[b'd'], sig[b's'], e))
       return False

dkim/dnsplug.py

@@ -27,6 +27,7 @@ __all__ = [
 
 def get_txt_dnspython(name, timeout=5):
     """Return a TXT record associated with a DNS name."""
+    import dkim
     try:
       a = dns.resolver.query(name, dns.rdatatype.TXT,raise_on_no_answer=False, lifetime=timeout)
       for r in a.response.answer:
@@ -34,6 +35,10 @@ def get_txt_dnspython(name, timeout=5):
               return b"".join(list(r.items)[0].strings)
     except dns.resolver.NXDOMAIN: pass
     except dns.resolver.NoNameservers: pass
+    except dns.resolver.NoResolverConfiguration as e:
+        raise dkim.DnsTimeoutError('dns.resolver.NoResolverConfiguration: {0}'.format(e))
+    except dns.exception.Timeout as e:
+        raise dkim.DnsTimeoutError('dns.exception.Timeout: {0}'.format(e))
     return None