Set the actual local port number to btrace.port system property

[trustin]

Motivation:

BTrace agent currently sets the port number given by a user to
btrace.port system property as-is. This behavior can be a problem
when:

• The agent actually failed to bind to the given port, because a user
  may still attempt to connect to the port number specified in
  btrace.port, where other server may be running already there.
• A user cannot know the actual port where BTrace agent is running when
  the user specified 0 as the port number, because we only know the
  actual port number after creating a server socket on it.

Modifications:

• Set the actual local port number after creating a ServerSocket so
  that a user can later figure out the actual port number even if the
  user specified 0 as the port number.

Result:

• A user can know the actual local port number, even when the user
  specified 0.
• A user can know the agent server socket is not open easily by checking
  the existence of btrace.port System property.

[jbachorik]

Can you, please, make sure you have OCA signed? https://oca.opensource.oracle.com/

[trustin]

I can't sign the OCA because it fails saying "You can't submit a new request unless the one that is pending signature is resumed or withdrawn." I indeed cancelled the DocuSign session because I realized my information in the Oracle account was outdated (wrong employer name and address). Now that I updated my information, but I can't sign anymore. 🤔

[trustin]

Could someone clean up my state so I can try again?

[trustin]

Alternatively, how about making the proposed change by yourself? It's just a one liner after all. I hereby release this changeset to the public domain (Creative Commons Zero 1.0).

[trustin]

@jbachorik I've just figured out how to do it by myself and signed the OCA. Could you please merge this and make it part of the next releases?

[jbachorik]

Great, I will merge this as soon as you appear in the list of signatories. I am afraid it can take a couple of days :(

[trustin]

Thanks, @jbachorik ! Looking forward to the next release. 🙇