Add "complete break ada" test to gdb.ada/complete.exp

This patch adds a new test to demonstrate a regression introduced by:

    commit b5ec771e
    Date:   Wed Nov 8 14:22:32 2017 +0000
    Subject: Introduce lookup_name_info and generalize Ada's FULL/WILD name matching

The original purpose of the new test is to exercise the "complete"
command with an expression for which a large number of matches are
returned and to verify that each match returned is a plausible match.
In this particular case, the commit above causes GDB to generate
additional matches which should in fact not appear in the list
(internally generated symbols, or symbols that should be enclosed
between "<...>"). These extraneous entries are easy to spot, because
they have uppercase characters, such as:

    break ada__stringsS
    break ada__strings__R11s
    [etc]

For now, the new test is KFAIL'ed, to avoid generating a new FAIL
while we work on fixing that regression.

gdb/testsuite/ChangeLog:

        PR gdb/22670
        * gdb.ada/complete.exp: Add "complete break ada" test.

Tested on x86_64-linux with GDB built before and after the patch
that caused the regression (b5ec771e).
The test passes before the regression, and generates a KFAIL after.