Use a timeout for docker list & stat cmds

closes #1133

etc/telegraf.conf

@@ -565,6 +565,8 @@
 #   endpoint = "unix:///var/run/docker.sock"
 #   ## Only collect metrics for these containers, collect all if empty
 #   container_names = []
+#   ## Timeout for docker list, info, and stats commands
+#   timeout = "5s"
 
 
 # # Read statistics from one or many dovecot servers
@@ -600,6 +602,9 @@
 #   ## Commands array
 #   commands = ["/tmp/test.sh", "/usr/bin/mycollector --foo=bar"]
 # 
+#   ## Timeout for each command to complete.
+#   timeout = "5s"
+# 
 #   ## measurement name suffix (for separating different commands)
 #   name_suffix = "_mycollector"
 #