Add '+' sign at the end of echo package

Summary:
-Fix lldb test failures introduced by r238530
-This fix TestGdbRemoteAuxvSupport.py and TestLldbGdbServer.py

Test Plan:
./dotest -p TestGdbRemoteAuxvSupport.py
./dotest -p TestLldbGdbServer.py

Reviewers: clayborg, chaoren, vharron

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D10116

llvm-svn: 238535