port missing changes from flannel to canal

Prevent remove of cni binaries when relation departs
- charmed-kubernetes/charm-flannel@ab06203

switch from flannel v0.11.0 to v0.20.2
- charmed-kubernetes/charm-flannel@16d6841#diff-898d34a6a1f3d1d0f111f88eafaac32fa26ef0ce51d41029d54a5b3f143bb3f8

reactive/flannel.py

@@ -171,13 +171,14 @@ def configure_network(etcd):
         }
     })
     cmd = "etcdctl "
-    cmd += "--endpoint '{0}' ".format(etcd.get_connection_string())
-    cmd += "--cert-file {0} ".format(ETCD_CERT_PATH)
-    cmd += "--key-file {0} ".format(ETCD_KEY_PATH)
-    cmd += "--ca-file {0} ".format(ETCD_CA_PATH)
-    cmd += "set /coreos.com/network/config '{0}'".format(data)
+    cmd += "--endpoints '{0}' ".format(etcd.get_connection_string())
+    cmd += "--cert {0} ".format(ETCD_CERT_PATH)
+    cmd += "--key {0} ".format(ETCD_KEY_PATH)
+    cmd += "--cacert {0} ".format(ETCD_CA_PATH)
+    cmd += "put /coreos.com/network/config '{0}'".format(data)
+    env = dict(os.environ, ETCDCTL_API="3")
     try:
-        check_call(split(cmd))
+        check_call(split(cmd), env=env)
         return True
 
     except CalledProcessError:
@@ -262,9 +263,6 @@ def cleanup_deployment():
              '/run/flannel/subnet.env',
              '/usr/local/bin/flanneld',
              '/usr/local/bin/etcdctl',
-             '/opt/cni/bin/flannel',
-             '/opt/cni/bin/bridge',
-             '/opt/cni/bin/host-local',
              '/etc/cni/net.d/10-flannel.conf',
              ETCD_KEY_PATH,
              ETCD_CERT_PATH,