Added order by query tests

- Added static order by tests to test_queries.py and QueryTest/sort.test
- test_order_by.py also contains tests with static queries that are run with
  multiple memory limits.
- Added stress, scratch disk and failpoints tests
- Incorporated Srinath's change that copied all order by with limit tests into
  the top-n.test file

Extra time required:

Serial:
scratch disk: 42 seconds
test queries sort : 77 seconds
test sort: 56 seconds
sort stress: 142 seconds
TOTAL: 5 min 17 seconds

Parallel(8 threads):
scratch disk: 40 seconds
test queries sort: 42 seconds
test sort: 49 seconds
sort stress: 93 seconds
TOTAL: 3 min 44 sec

Change-Id: Ic5716bcfabb5bb3053c6b9cebc9bfbbb9dc64a7c
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2820
Reviewed-by: Taras Bobrovytsky <tbobrovytsky@cloudera.com>
Tested-by: jenkins