Add base 'enable/disable invalid location range' tests

Add base 'enable/disable invalid location range' tests

This adds tests that exercise the "bad breakpoint number" paths.
Specifically:

 - malformed ranges
 - use of explicit 0 as bp/loc number.
 - inverted ranges

I'm adding this as a baseline to improve.  This shows that there's a
lot of inconsistency in GDB's output (e.g., "bad" vs "Bad").

Also, IMO, the "0-0" and inverted range cases should be loud errors.

That and more will all be addressed in the next patch.

gdb/testsuite/ChangeLog:
2017-11-07  Pedro Alves  <palves@redhat.com>

	* gdb.cp/ena-dis-br-range.exp: Add tests.