Remove '/' from target filepath

os.path.join ignore previous parameters if one starts with '/'. All
targets start with '/', making updated_targets to try to open a file in
the root folder in case of a unix system.
Minor edits to basic_client.py.
Fix indentation

Indentation is with 2 spaces
Merge branch 'filepath' of https://github.com/meskio/tuf into meskio-filepath
Review and update Pull Request #232.

Fix test conditions for updated_targets(), which incorrectly verified the expected number of updated targets with assertTrue().

Update comment for PR fix to clarify os.path.join() behavior and the expected file paths.
Merge pull request #233 from vladimir-v-diaz/meskio-filepath

Review and Update Pull Request #232