[jvm] add prefix option

[masarasi]

The mackerel-plugin-jvm monitors the application specified in --javaname, but there is an issue that it can only monitor one of the applications if there are multiple applications with the same name. I would like to solve this issue by making it possible to use --metric-key-prefix and --metric-label-prefix.

# /usr/local/bin/mackerel-plugin-jvm -javaname Bootstrap -metric-key-prefix tomcat-ex -metric-label-prefix tomcat-ex --pidfile /usr/local/src/tomcat-ex/temp/tomcat.pid
jvm.tomcat-ex.new_space.NGCMX	1025507328.000000	1731999116
jvm.tomcat-ex.new_space.NGC	35651584.000000	1731999116
jvm.tomcat-ex.new_space.EU	18874368.000000	1731999116
jvm.tomcat-ex.new_space.S0U	0.000000	1731999116
jvm.tomcat-ex.new_space.S1U	4194304.000000	1731999116
jvm.tomcat-ex.old_space.OGCMX	1025507328.000000	1731999116
jvm.tomcat-ex.old_space.OGC	31457280.000000	1731999116
jvm.tomcat-ex.old_space.OU	5605888.000000	1731999116
jvm.tomcat-ex.metaspace.MCMX	1140850688.000000	1731999116
jvm.tomcat-ex.metaspace.MCMN	0.000000	1731999116
jvm.tomcat-ex.metaspace.MC	13369344.000000	1731999116
jvm.tomcat-ex.metaspace.MU	13096038.400000	1731999116
jvm.tomcat-ex.metaspace.CCSC	1507328.000000	1731999116
jvm.tomcat-ex.metaspace.CCSU	1363046.400000	1731999116
jvm.tomcat-ex.memorySpace.oldSpaceRate	17.820638	1731999116
jvm.tomcat-ex.memorySpace.newSpaceRate	64.705882	1731999116
jvm.tomcat-ex.gc_events.YGC	0.000000	1731999116
jvm.tomcat-ex.gc_events.FGC	0.000000	1731999116
jvm.tomcat-ex.gc_events.CGC	0.000000	1731999116
jvm.tomcat-ex.gc_time.YGCT	0.000000	1731999116
jvm.tomcat-ex.gc_time.FGCT	0.000000	1731999116
jvm.tomcat-ex.gc_time.CGCT	0.000000	1731999116
jvm.tomcat-ex.gc_time_percentage.YGCT	0.000000	1731999116
jvm.tomcat-ex.gc_time_percentage.FGCT	0.000000	1731999116
jvm.tomcat-ex.gc_time_percentage.CGCT	0.000000	1731999116

# MACKEREL_AGENT_PLUGIN_META=1 /usr/local/bin/mackerel-plugin-jvm -javaname Bootstrap -metric-key-prefix tomcat-ex -metric-label-prefix tomcat-ex --pidfile /usr/local/src/tomcat-ex/temp/tomcat.pid | grep -v "mackerel-agent-plugin" | jq
{
  "graphs": {
    "jvm.tomcat-ex.gc_events": {
      "label": "JVM tomcat-ex GC events",
      "unit": "integer",
      "metrics": [
        {
          "name": "YGC",
          "label": "Young GC event",
          "stacked": false
        },
        {
          "name": "FGC",
          "label": "Full GC event",
          "stacked": false
        },
        {
          "name": "CGC",
          "label": "Concurrent GC event",
          "stacked": false
        }
      ]
    },

• https://mackerel.io/orgs/masarasi-org/hosts/5edmqp8NvZ3/-/graphs/custom.jvm.tomcat.memorySpace.*#period=30m
• https://mackerel.io/orgs/masarasi-org/hosts/5edmqp8NvZ3/-/graphs/custom.jvm.tomcat-ex.memorySpace.*#period=30m

[yohfee]

Thanks! implementation seems good.

It is better to have

• Descriptions about their usage on README
• Tests that keys and labels are replaced as expected