Minor updates to requirement files.
Allow partial metadata to be properly loaded with zero good signatures.

Previously, the repository tool allowed partial metadata to be written with zero good signatues and later successfully loaded.  However, the partial metadata was not properly marked by load_repository().  The 'partial_loaded' flag is now set (if partial metadata is written with zero good signatures) and matches the behavior of partial_write().
Increase sleep time after starting simple server in integration tests.
Cosmetic edits to repository_lib.py.
Merge pull request #220 from vladimir-v-diaz/develop

Allow proper loading of partial metadata, update requirement files, and minor edits to repository_lib.py and integration tests.