nativesdk-ncurses 5.9: files were installed but not shipped

There is an warning:

$ bitbake nativesdk-ncurses

WARNING: QA Issue: nativesdk-ncurses: Files/directories were installed
but not shipped
  /opt/poky/1.3+snapshot/sysroots/i686-pokysdk-linux/usr/bin/clear.ncurses
  /opt/poky/1.3+snapshot/sysroots/i686-pokysdk-linux/usr/bin/reset.ncurses
NOTE: Tasks Summary: Attempted 533 tasks of which 521 didn't need to be
rerun and all succeeded.

And there is no clear or reset tool in the SDK.

This is caused by:
ALTERNATIVE_ncurses-tools = "clear reset"

It creates clear.ncurses and reset.ncurses which are used for avoiding
the conflicts with the target busybox, but SDK doesn't need them since
there is no nativesdk-busybox (then no conflicts), so:

ALTERNATIVE_ncurses-tools_class-target = "clear reset"

will fix the problem.

[YOCTO #3325]

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
change the prompt to indicate env has been sourced