sshcontrol.py: Add methods to copy dirs and delete files

sshcontrol.py: Add methods to copy dirs and delete files

This patch add new methods to SSHControl class. These methods
include:
    - Copy a dir to DUT
    - Delete a file in the DUT
    - Delete a directory in the DUT (if empty)
    - Delete a directory structure in the DUT

[YOCTO #9565]

Signed-off-by: Mariano Lopez <mariano.lopez@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>