don't use directory in test name

I noticed that a few tests in completion.exp put the directory name
into the name of the resulting test.  While the directory name is
relative, this still makes for spurious differences depending on
whether the test was run in serial or parallel mode.

This patch fixes the problem.  I'm checking it in.

2014-06-12  Tom Tromey  <tromey@redhat.com>

	* gdb.base/completion.exp: Don't use directory name in test.