Avoid zeroing of test files if source and dest are same

During call to copy_dir, if by mistake, testbed.py has incorrect host_build
parameter, then the contrail-test files are getting copied onto itself.
This causes them to get erased.
To avoid this, check for local and remote host being same, then local
and remote dir being same. In such case, avoid copying the
contrail-test files

Change-Id: Ie9ff05f6f5857e7f06188c94e3438ba325b8e48f