RFR: 8262520: Add CLHSDB command to connect to debug server [v2]

[Yasumasa Suenaga]

> `attach` command on CLHSDB supports to attach live process (PID) and coredump, but it cannot connect to debug server. CLHSDB does not have a command to connect to debug server.
> 
> Other jhsdb commands (jstack, jmap, etc...) can connect debug server via `--connect` option, so CLHSDB should connect to it.
> 
> After this change, you can connect to debug server with 'connect <hostname>'.

Yasumasa Suenaga has updated the pull request incrementally with one additional commit since the last revision:

  Implement as "attach" instead of "connect"

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2773/files
  - new: https://git.openjdk.java.net/jdk/pull/2773/files/7e86add8..e59bb9c7

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2773&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2773&range=00-01

  Stats: 101 lines in 5 files changed: 35 ins; 25 del; 41 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2773.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2773/head:pull/2773

PR: https://git.openjdk.java.net/jdk/pull/2773