Fix regexp quoting in gdb.ada test cases

I noticed that some gdb.ada tests used regular expressions like:

         "Continuing\..*$inferior_exited_re.*" \

Here, the "\." should either be "." or "\\." -- "\." is not really
meaningful.

This patch fixes all the cases of this I could find in gdb.ada.  In
one test (fun_renaming.exp), using "\\." would result in failures, and
here I rewrote the tests to use -wrap.

Approved-By: Andrew Burgess <aburgess@redhat.com>