run sh instead of bash in StreamIn

Signed-off-by: Simon Leung <leungs@us.ibm.com>
ensure /home exists before creating user

also detect whether to use bash or sh as login shell

Signed-off-by: Simon Leung <leungs@us.ibm.com>
ensure /tmp is writable in container

also clean up /tmp/warden-host, which used to leak from the pivot_root
dance

Signed-off-by: Simon Leung <leungs@us.ibm.com>
fixup Dockerfile, update to Go 1.3.1

Signed-off-by: Simon Leung <leungs@us.ibm.com>
add wshd tests for /tmp chmodding and cleanup

Signed-off-by: Simon Leung <leungs@us.ibm.com>