Optimize data collection.

[simonnagl]

trafficstars

The JMX API supports to query multiple attributes of one MBean with one request. We should support that too.

Needed research:

• Does this improve performance?
• Is using getAttributes slower if only fetching one attribute?

Needed changes:

• Extend MBeanQueryInfo: MBeanQueryInfo should contain information about the MBean and a list of Attributes to collect and where to store them.
• Change initialization of MBeanServerCollector to fit.
• Change data collection of MBeanServerColletor to fit.

[simonnagl]

Migrated to https://github.com/firehol/netdata/issues/2792

[simonnagl]

Emigrated from netdata/netdata#2792