ci: Use dedicated slave instead of Docker

Using a dedicated slave node instead of a Docker container has a few
advantages:

* Persistent configuration is possible, without making weird assumptions
  (e.g. Jenkins UID/GID) in the Dockerfile
* Can limit concurrent deployments by controlling executor count on the
  node

ci/Dockerfile

@@ -1,14 +0,0 @@
-FROM fedora:27
-
-RUN dnf install -y \
-	ansible \
-	openssh-clients \
-	python2-netaddr
-
-# XXX These UID/GIDs must match the Jenkins UID/GID on the agent
-RUN groupadd -g 992 jenkins
-RUN useradd -u 995 -g jenkins -c Jenkins -d /var/lib/jenkins -m jenkins
-
-RUN install -m 700 -o jenkins -g jenkins -d /var/lib/jenkins/.ssh
-COPY known_hosts /var/lib/jenkins/.ssh/
-RUN chown jenkins:jenkins /var/lib/jenkins/.ssh/known_hosts

ci/dch-gw.jenkinsfile

@@ -2,9 +2,7 @@
 
 pipeline {
     agent {
-        dockerfile {
+        label 'ansible'
-            dir 'ci'
-        }
     }
 
     triggers {

ci/known_hosts

@@ -1,3 +0,0 @@
-172.31.0.1 ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIFQJj11B1OqSfx/OHkJ5rzwk6ENLjMgfaVfkYC6xc7Ly
-dc0.pyrocufflink.blue ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAILnQc6ySo4twuKSx3JRQng4LufIC9beOWe7MvyfzVdNH
-dc1.pyrocufflink.blue ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIMS87Xa5C3AS7Pum2GwT9DnZFP34gaRE59w0G2oa8+EO

ci/samba-dc.jenkinsfile

@@ -2,9 +2,7 @@
 
 pipeline {
     agent {
-        dockerfile {
+        label 'ansible'
-            dir 'ci'
-        }
     }
 
     triggers {