Added gdb-remote memory read ($m) test.

Added set-memory:{content} and get-memory-address-hex: commands
to the test exe for gdb-remote.  Added a test that sets the content
via the inferior command line, then reads it back via gdb-remote
with $m.

Passing on debugserver.  Marked as fail on llgs.  Implementing
in the llgs branch next.

llvm-svn: 210116