Add 'qXfer:features:read' to known stub list

Summary:
-Fix darwin bot failure "unknown qSupported stub feature reported: qXfer:features:read"
-TestGdbRemoteAuxvSupport.py and TestLldbGdbServer.py were affected by this problem

Test Plan:
dotest.py -m --executable /Users/lldb_build/testSlave/buildDir/lldb.src/build/Debug/lldb --framework /Users/lldb_build/testSlave/buildDir/lldb.src/build/Debug/LLDB.framework -A x86_64 -C clang -p TestLldbGdbServer.py
dotest.py -m --executable /Users/lldb_build/testSlave/buildDir/lldb.src/build/Debug/lldb --framework /Users/lldb_build/testSlave/buildDir/lldb.src/build/Debug/LLDB.framework -A x86_64 -C clang -p TestGdbRemoteAuxvSupport.py

Reviewers: clayborg, sivachandra, vharron

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D10043

llvm-svn: 238262