Bad table name on master_create_distributed_table()

This fix handles when master_create_distributed_table is called with
a an index as the first argument. More generally, it is called with
a relation that is not ordinary table or foreign table.
Improvements on style

This commit aims to improve coding style to fit our coding conventions.
Also, error message is updated wrt postgres error message guide.
Final style changes

Minor variable naming/error style fixes.
Add test for new path

This exercises the logic that rejects distribution of indexes.
Merge pull request #36 from citusdata/feature-issue#13

Bad table name on master_create_distributed_table()

cr: @sumedhpathak and @jasonmp85