Add --cwd parameter to set debuggee working directory in lldbclient

Setting the working direcotry is useful for binaries that expect to be
run from a specific folder. In particular, this allows to debug target
integration tests with data files, since they expect these files to be
available by relative paths.

Test: lldbclient.py /data/ -r pwd # prints /
      lldbclient.py --cwd /data/ -r pwd # prints /data
      lldbclient.py --cwd /data/ --chroot / -r pwd # exits with error
      lldbclient.py --cwd /invalid_path -r pwd # exits with error
Change-Id: I9d1002c28219028d0120df3b9620e09030d1361e
2 files changed