Keyword to report failures due to a known bug

Keyword to report failures due to a known bug

Use the keyword in the [Teardown] configuration line of the
affected test to get a pretty report about a Bugzilla bug
that is causing the test to fail (and also an indication
that the failure is expected).

This shall be used instead of various ad-hoc kludges to hit
a particular known bug but still continue the test suite.
At least one future test suite needs this and there might
be others.

The change was originally committed as a8248ecaf however
that change has messed up commit message, obscuring the
real purpose of changes. Additionally, the keyword was
not run through robot.tidy and it clobbers the original
test failure message. This update makes sure that the
original failure message is shown as well as the message
about the URL of the bug that is causing the failure so
the exact problem can be spotted without digging in
log.html.

Change-Id: Id32850307f68160b63247dd97a1ffaa8203bb1bc
Signed-off-by: Jozef Behran <jbehran@cisco.com>