Mock improvements

Mock providers:

• Fixed support for joining data for the same block from many mock files
• Added sanity check for data read from mock file
• Replace listdir with walk to scan all subdirectories of given mock dir.
• Removed usused imports and loggers. Common methods moved to base class

Mock files:

• Mock files cleanup.
• Mock data for vops related tests.
• Use mock vops data in sync.

Bug fixes:

• Fix for RowProxy object does not support item assignment if post category is empty.

Other changes:

• Enable reputation update on live sync
• Refresh sparse stats before exiting due to block limit exceeded
• Update tests to take mock vops into account