ext-sdk-prepare.py: exclude do_rm_work from unexpected output; create unit test
When installing the esdk with INHERIT += "rm_work", the script complains
about do_rm_work as unexpected output from the bitbake run. This patch
ignores any output lines with do_rm_work and further refactors the
output comparison into its own function creates a new unit test to
verify the fix. The unit test can be run direct from the command line or
via oe-selftest.
[YOCTO #9019]
Signed-off-by: Bill Randle <william.c.randle@intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
