Fix object name for query in Tomcat metrics

[izeye]

This PR fixes object name for query in Tomcat metrics.

Closes gh-1754

[izeye]

I'm not sure why the following tests have been failed on JDK 10, especailly Jetty one:

io.micrometer.core.instrument.binder.jetty.JettyServerThreadPoolMetricsTest > threadMetrics() FAILED
    java.lang.AssertionError: 
    Expecting:
     <0.0>
    not to be equal to:
     <0.0>
        at io.micrometer.core.instrument.binder.jetty.JettyServerThreadPoolMetricsTest.threadMetrics(JettyServerThreadPoolMetricsTest.java:65)

io.micrometer.core.instrument.binder.tomcat.TomcatMetricsTest > mbeansAvailableAfterBinder() FAILED
    org.opentest4j.AssertionFailedError: 
    Expecting:
     <3.0>
    to be equal to:
     <1119.0>
    but was not.
        at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
        at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
        at io.micrometer.core.instrument.binder.tomcat.TomcatMetricsTest.checkMbeansAfterRequests(TomcatMetricsTest.java:235)
        at io.micrometer.core.instrument.binder.tomcat.TomcatMetricsTest.lambda$mbeansAvailableAfterBinder$1(TomcatMetricsTest.java:159)
        at io.micrometer.core.instrument.binder.tomcat.TomcatMetricsTest.runTomcat(TomcatMetricsTest.java:210)
        at io.micrometer.core.instrument.binder.tomcat.TomcatMetricsTest.mbeansAvailableAfterBinder(TomcatMetricsTest.java:144)

347 tests completed, 2 failed, 2 skipped

[izeye]

Rerunning the build has been passed. There seems to be some flakiness, but I'm not sure how.