Check if it's possible to start Spring Boot on a JVM that doesn't have JMX

If you run in a restricted JVM that has no JMX, Micrometer falls in a heap:

Caused by: java.lang.NoClassDefFoundError: Could not initialize class sun.management.ManagementFactoryHelper
	at java.lang.management.ManagementFactory.getMemoryPoolMXBeans(ManagementFactory.java:387) ~[na:1.8.0_102-internal]
	at io.micrometer.core.instrument.binder.jvm.JvmGcMetrics.<init>(JvmGcMetrics.java:76) ~[micrometer-core-1.3.2.jar!/:1.3.2]
	at io.micrometer.core.instrument.binder.jvm.JvmGcMetrics.<init>(JvmGcMetrics.java:72) ~[micrometer-core-1.3.2.jar!/:1.3.2]
	at org.springframework.boot.actuate.autoconfigure.metrics.JvmMetricsAutoConfiguration.jvmGcMetrics(JvmMetricsAutoConfiguration.java:48) ~[spring-boot-actuator-autoconfigure-2.2.4.RELEASE.jar!/:2.2.4.RELEASE]

Seems like we could be more defensive, but this is probably not the end of the problem. E.g. I found (from running the Petlinic in Tiny Core Linux) that eh-cache fails in the same way. Also webjars locator has an out of date dependency on the classgraph dependency, and that fails unless you update it.

Start with the stack trace through io.micrometer.core.instrument.binder.jvm.JvmGcMetrics and org.springframework.boot.actuate.autoconfigure.metrics.JvmMetricsAutoConfiguration, then reproduce startup on a JVM without JMX. Investigate the related eh-cache and webjars locator failures mentioned in the issue, and define done as establishing the supported behavior and affected startup paths.