Refactor jdwp_provider to make it easier to change the default

Change JdwpProvider to have a kDefaultJdwpProvider member that can be
updated to be whatever the current default jdwp provider is.

Test: build
Test: cmdline_parser_test
Change-Id: I89559cc63d371be60b594d850f1a16a557b42edc
3 files changed