tox: bump the pylint version to 2.6.0 in the default run (#544)

Changes:

tox: bump the pylint version to 2.6.0 in the default run
Fix pylint 2.6.0 W0707 warnings (raise-missing-from)

3 files changed, 9 insertions, 7 deletions

diff --git a/cloudinit/distros/__init__.py b/cloudinit/distros/__init__.py
index effb4276..2537608f 100755
--- a/cloudinit/distros/__init__.py
+++ b/cloudinit/distros/__init__.py
@@ -607,10 +607,11 @@ class Distro(metaclass=abc.ABCMeta):
         lock_tools = (['passwd', '-l', name], ['usermod', '--lock', name])
         try:
             cmd = next(tool for tool in lock_tools if subp.which(tool[0]))
-        except StopIteration:
+        except StopIteration as e:
             raise RuntimeError((
                 "Unable to lock user account '%s'. No tools available. "
-                "  Tried: %s.") % (name, [c[0] for c in lock_tools]))
+                "  Tried: %s.") % (name, [c[0] for c in lock_tools])
+            ) from e
         try:
             subp.subp(cmd)
         except Exception as e:
diff --git a/cloudinit/distros/arch.py b/cloudinit/distros/arch.py
index 038aa9ac..967be168 100644
--- a/cloudinit/distros/arch.py
+++ b/cloudinit/distros/arch.py
@@ -61,9 +61,9 @@ class Distro(distros.Distro):
     def _write_network_config(self, netconfig):
         try:
             return self._supported_write_network_config(netconfig)
-        except RendererNotFoundError:
+        except RendererNotFoundError as e:
             # Fall back to old _write_network
-            raise NotImplementedError
+            raise NotImplementedError from e
 
     def _write_network(self, settings):
         entries = net_util.translate_network(settings)
diff --git a/cloudinit/distros/parsers/resolv_conf.py b/cloudinit/distros/parsers/resolv_conf.py
index 299d54b5..62929d03 100644
--- a/cloudinit/distros/parsers/resolv_conf.py
+++ b/cloudinit/distros/parsers/resolv_conf.py
@@ -150,9 +150,10 @@ class ResolvConf(object):
                 tail = ''
             try:
                 (cfg_opt, cfg_values) = head.split(None, 1)
-            except (IndexError, ValueError):
-                raise IOError("Incorrectly formatted resolv.conf line %s"
-                              % (i + 1))
+            except (IndexError, ValueError) as e:
+                raise IOError(
+                    "Incorrectly formatted resolv.conf line %s" % (i + 1)
+                ) from e
             if cfg_opt not in ['nameserver', 'domain',
                                'search', 'sortlist', 'options']:
                 raise IOError("Unexpected resolv.conf option %s" % (cfg_opt))