Add ToolProvider interface implementation keytool

[Wojtek]

Hello,
Move to strongly encapsulate JDK internals (i.e. JEP-403 and 396) affected access to generating 
self-signed certificates. JEP itself states:

 > Code that uses the sun.security.tools.keytool.CertAndKeyGen class to generate self-signed 
certificates. There is not yet a standard API for this functionality (though a request has been 
submitted [1]); in the mean time, developers can use existing third-party libraries that include 
this functionality.

However, linked issue [1] was just closed with "wontfix" status:

 > Closing as "Won't Fix". We have no plans to provide APIs for creating certificates. The "keytool 
-gencert" option can be used to create certificates and is the only mechanism that we will support.

While using 'keytool' can be OK, it was brought to my attention existence of 
`java.util.spi.ToolProvider` interface that would help avoid starting new VM.

Would it be possible/could be considered to add implementation of ToolProvider to the `keytool`?


[1] https://bugs.openjdk.java.net/browse/JDK-8058778
-- 
Wojtek