ktest: Add SCP_TO_TARGET_INSTALL option

Currently the option used to scp both the modules to the target as well
as the kernel image are the same (SCP_TO_TARGET). But some embedded
boards may require them to be different. The modules may need to be put
directly on the board, but the kernel image may need to go to a
tftpserver.

Add the option SCP_TO_TARGET_INSTALL that will allow the user to change
the config so that they may have the modules and image got to different
machines.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>