Dyanamo Table.scan() should accept 'attributes' argument
Add EC2 associate_address_object method

Fixes #1874, #1893.
Adding unit test for table scan on specific attrs
Make sure associate address failure returns false

Modifies EC2 connection to use common code for both associate_address and
associate_address_object. False is now properly returned for associate_address
again, keeping backward compatibility.
Merge remote-tracking branch 'stevearc/scan_attributes' into develop

Fixes #1945.

Conflicts:
	boto/dynamodb2/table.py
Merge pull request #1967 from danielgtaylor/ec2-address

Add EC2 associate_address_object method. Fixes #1874, #1893, #1967.
Added attributes support to ``get_item``.
Fixes #1643 & #1877
Added a missing docstring.

:sweat:
Merge branch 'ddb-get-item-attrs' into develop
Fixes #1972