Fix URL replacement in BaseOpenStackMockTest

This PR fixes the replacement of service URL strings containing spaces. How many of us have spent hours trying to debug something all because of a space? ;)
Not checking for the `:` any more? is that intentional? Could you also add a comment along the lines of "support patterns with spaces such as `    "  URL`"?

Also, if this is called often, perhaps consider pulling the pattern out into a `urlTokenPattern` constant and using
```
urlTokenPattern.matcher(new String(response.getBody())).replaceAll(" \"" + url.toString());
```
instead? I'm guessing from the above import that you may have been thinking about that too..? ;-)