Add an option ACTIVE_SEGMENT_COUNT for readable external tables to limit number of logical segments to execute a query with readable external tables. Fragments will be distributed across only limit number of segments.
Add integration tests for fragments distribution;
Modify test environment adding additional segment host;
Fix other integration tests because of the changing test environment.
ACTIVE_SEGMENT_COUNTfor readable external tables to limit number of logical segments to execute a query with readable external tables. Fragments will be distributed across only limit number of segments.