[Android] Exclude the gdbserver from release mode of packaging tool.

The gdbserver is used for debugging XWalk, which should not be included
in the release binary of packaging tool. Because it would introduce additional size
of the binary.

So exclude gdbserver binary from release version and leave it for debug version
the same as that for xwalk_core_library.
Merge pull request #1289 from junmin-zhu/gdb

[Android] Exclude the gdbserver from release mode of packaging tool.