Merge ~oddbloke/cloud-init/+git/cloud-init:nested_set into cloud-init:master

[Dan Watkins]

cc_rsyslog: Escape possible nested set

Under Python 3.7, we are seeing `FutureWarning: Possible nested set at
position 23`; escaping this bracket causes that warning to disappear.

LP: #1816967

[Server Team CI bot (server-team-bot)]

FAILED: Continuous integration, rev:d6a8772f3f20b58e2b5ab1b9669083b5952e8583
https://jenkins.ubuntu.com/server/job/cloud-init-ci/574/
Executed test runs:
    SUCCESS: Checkout
    SUCCESS: Unit & Style Tests
    SUCCESS: Ubuntu LTS: Build
    FAILED: Ubuntu LTS: Integration

Click here to trigger a rebuild:
https://jenkins.ubuntu.com/server/job/cloud-init-ci/574/rebuild

review: Needs Fixing (continuous-integration)

[Server Team CI bot (server-team-bot)]

FAILED: Continuous integration, rev:d6a8772f3f20b58e2b5ab1b9669083b5952e8583
https://jenkins.ubuntu.com/server/job/cloud-init-ci/575/
Executed test runs:
    SUCCESS: Checkout
    SUCCESS: Unit & Style Tests
    SUCCESS: Ubuntu LTS: Build
    FAILED: Ubuntu LTS: Integration

Click here to trigger a rebuild:
https://jenkins.ubuntu.com/server/job/cloud-init-ci/575/rebuild

review: Needs Fixing (continuous-integration)

[Server Team CI bot (server-team-bot)]

PASSED: Continuous integration, rev:d6a8772f3f20b58e2b5ab1b9669083b5952e8583
https://jenkins.ubuntu.com/server/job/cloud-init-ci/576/
Executed test runs:
    SUCCESS: Checkout
    SUCCESS: Unit & Style Tests
    SUCCESS: Ubuntu LTS: Build
    SUCCESS: Ubuntu LTS: Integration
    IN_PROGRESS: Declarative: Post Actions

Click here to trigger a rebuild:
https://jenkins.ubuntu.com/server/job/cloud-init-ci/576/rebuild

review: Approve (continuous-integration)

[Ryan Harper (raharper)]

review: Approve

diff --git a/cloudinit/config/cc_rsyslog.py b/cloudinit/config/cc_rsyslog.py
index 27d2366..22b1753 100644
--- a/cloudinit/config/cc_rsyslog.py
+++ b/cloudinit/config/cc_rsyslog.py
@@ -203,7 +203,7 @@ LOG = logging.getLogger(__name__)
 COMMENT_RE = re.compile(r'[ ]*[#]+[ ]*')
 HOST_PORT_RE = re.compile(
     r'^(?P<proto>[@]{0,2})'
-    r'(([[](?P<bracket_addr>[^\]]*)[\]])|(?P<addr>[^:]*))'
+    r'(([\[](?P<bracket_addr>[^\]]*)[\]])|(?P<addr>[^:]*))'
     r'([:](?P<port>[0-9]+))?$')