title: custom grok patterns not work
body: <p>In telegraf logparser,my config segment like this:</p>
  
  <pre><code>[[inputs.logparser]]
     files = ["/home/work/local/monitor/logs/xxx.log"]
     from_beginning = false
     watch_method = "inotify"
     [inputs.logparser.grok]
       patterns = ["%{LOG_LINE}"]
       measurement = "xxx_log"
       custom_pattern_files = ["/etc/telegraf/patterns_xxx.conf"]
       timezone = "UTC"
  </code></pre>
  
  <p>log like this </p>
  
  <pre><code>"a:b"
  "c=d"
  </code></pre>
  
  <p>my custom patterns：</p>
  
  <pre><code>PATTERN1 %{WORD:key}:%{WORD:value}
  PATTERN2 %{WORD:key}=%{WORD:value}
  LOG_LINE %{PATTERN1}|%{PATTERN2}
  </code></pre>
  
  <p>for log:</p>
  
  <pre><code>name=jack
  </code></pre>
  
  <p>LOG_LINE got</p>
  
  <pre><code>{"key": [["a",null]],"value": [["b",null]]}
  </code></pre>
  
  <p>but i want to get</p>
  
  <pre><code>{"key": ["a"],"value": ["b"]}
  </code></pre>
  
  <p>what is the correct pattern ? Thanks!</p>