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.


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@210116 91177308-0d34-0410-b5e6-96231b3b80d8