Increase the gdb-remote packet timeout for the first packet we send

Increase the gdb-remote packet timeout for the first packet we send
to the remote side (QStartNoAckMode) - it may take a little longer
than normal to get a reply.

In debugserver, hardcode the priority for several threads so they
aren't de-prioritized when a user app is using system resources.
Also, set the names of the threads.

<rdar://problem/17509866>

llvm-svn: 213828