Modify TestSettings test for stderr.txt/stdout.txt to ignore an
optional path prior to the file base name.

On Linux x86_64 (Ubuntu 12.04) I am sometimes getting a full path
on the stderr.txt.  This changes the test for target.error-path and
target.output-path settings to ignore any optional directory before
the expected file base name.



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@207272 91177308-0d34-0410-b5e6-96231b3b80d8