Add support for using gdbserver with run-test

This will allow one to use alternative gdb frontends with run-test
tests by pointing them at the gdbserver port.

Test: ./test/run-test --host --64 --gdbserver 001-HelloWorld
      Use VSCode to attach to localhost:5039 and debug dalvikv64

Change-Id: I87f31f035d4192e786b152be43d8415dc7e0f210