test fix: TestLoadUsingPaths should use realpath

Summary:
TestLoadUsingPaths will fail if the build directory has
symlinks in its path, because the real paths reported by
the debugger won't match the symlink-laden paths it's expecting.

This can be solved just by using os.path.realpath on the base
path for the test.

Reviewers: JDevlieghere, jasonmolenda, labath

Reviewed By: JDevlieghere

Subscribers: lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D68618

llvm-svn: 374007