Normalize path for finding api_samples dir

When nova/tests/integrated and doc/api_samples are installed
in different subtrees and are only combined via symlinks,
running test_api_sample fails due to traversing into the
wrong tree. Use path normalization to avoid this problem.

Fixes: LP Bug #1186775

Change-Id: Ibe9e2442dc9bf3ba7bcb429cbac124dcaeea2cef
Merge "Normalize path for finding api_samples dir"