CQLSH doesn't exit with proper code with multiple SOURCE directives.

When I have the following files;

# master.sql

CREATE TABLE asdf (  id text,  primary key (id));

# a.sql

SOURCE './master.sql';

CREATE TABLE asdf (  id text,  primary key (id));

# b.sql

SOURCE './a.sql';

 
and execute

cqlsh --keyspace example --file ./b.sql

I don't get returned the proper status code. This happens because when multiple SOURCE commands are chained together like in the example above, the error doesn't get passed through to the final 'shell'. 

Subshell that needs to pass the statement error value to the parent shell: https://github.com/apache/cassandra/blob/trunk/bin/cqlsh.py#L1776
final statement error check which returns the parent shell statement error: https://github.com/apache/cassandra/blob/trunk/bin/cqlsh.py#L2474