Rename test/tools/lldb-gdbserver to test/tools/lldb-server

As requested in http://reviews.llvm.org/D7545 this change moves test/tools/lldb-gdbserver to test/tools/lldb-server ot match the name of the target being tested.

Differential Revision: http://reviews.llvm.org/D8061

llvm-svn: 231479