Ensure Weblogic and Websphere JMX are covered

To ensure an MBeanServer is available when needed you have to
look in JNDI before resorting to the JDK platform factory.

I had to copy some private code from Spring, but it seems
worth it.

Fixes gh-1092
Ignore test that is WIP
Re-instate test when fixed
DataSource metrics

This commit adds an abstraction that provides a standard manner to
retrieve various information that are shared by most data sources.

DataSourceInfo is implemented by the three data source implementations
that boot supports out-of-the-box: Tomcat, Hikari and Commons dbcp.

This abstraction is used to provide two additional metrics per data
source defined in the application: the number of allocated
connection(s) and the current usage of the connection pool.

Additional DataSourceInfo implementations for other data source types
can be added very easily, check DataourceInfoProvidersConfiguration
for more details.

Fixes gh-1013