gdbserver_tests filter out and don't expect empty lines.

Some filters might have left some empty lines in the output.  Filter them
out explicitly and don't expect any empty lines in any of the .exp files.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@14381 a5019735-40e9-0310-863c-91ae7b9d1cf9