Add support for using 'art' tools with gdbserver

Some tools (like run-jdwp-tests) invoke the 'art' tool automatically.
This makes it difficult to debug the runtime when running code
controlled by those tools. To allow this I added a --gdbserver flag to
both the 'art' tool and the 'run-jdwp-tests.sh' script.

To use:
    % ./art/tools/run-jdwp-tests.sh --debug \
                                    <...> \
                                    --gdbserver localhost:9999
or
    % art --gdbserver localhost:9999 <...>

In another terminal:
    % gdb /path/to/dalvikvm # the art command will print the
                            # appropriate path
    (gdb) target remote localhost:9999

Test: Manual
Change-Id: Ice9a9f7622eee66261d10663c83bf06aef95f399
2 files changed