Get File Wrong Content-Type Bug Fix

JIRA: CBDEUCE_99
- Bug Fix: Missed updating size when the file span multiple pages in Mongo
Get File Wrong Content-Type Bug Fix

JIRA: CBDEUCE_99
- Metadata Abstract driver was missing a function relied on by the rest of the system that was implemented by all drivers
Get File Wrong Content-Type Bug Fix

JIRA: CBDEUCE_99
- Use application/octet-stream instead of application/binary as application/binary is not an official MIME Type
Get File Wrong Content-Type Bug Fix

JIRA: CBDEUCE_99
- Added test in the vault model for the file length of an empty file
Get File Wrong Content-Type Bug Fix

JIRA: CBDEUCE_99
- Enhancement: MongoDB - removed check on length as we should be reasonably sure the value is there since it's added as zero (0) in create and updated in finalize file.
- pep8 compliance (per test/api/base.py)