tools/Coverity: Audit of MISSING_BREAK defects

tools/Coverity: Audit of MISSING_BREAK defects

Coverity uses several heuristics to identify when one case statement
legitimately falls through into the next, and a comment as the final item in a
case statement is one heuristic (the assumption being that it is a
justification for the fallthrough).

Use this to perform an audit of defects and hide the legitimate fallthroughs.

There are two bugfixes identified in the audit, both minor:
 * 'n' command line handling for gtracestat
 * BKSPC handling in xentop

All other identified defaults are legitimate fallthoughs

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Coverity-IDs: 1055464, 1055465, 1055467, 1055468, 1055481, 1055482
CC: Ian Campbell <Ian.Campbell@citrix.com>
CC: Ian Jackson <Ian.Jackson@eu.citrix.com>
CC: Wei Liu <wei.liu2@citrix.com>
CC: Xen Coverity Team <coverity@xen.org>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Don Koch <dkoch@verizon.com>