valgrind for system tests

[Dimitar Misev]

Add a systemtest/testcases_mandatory/test_memory_leaks/test.sh script that will run same as test_select, but use the following instead of rasql:

valgrind --tool=memcheck --leak-check=full --track-origins=yes directql ..

In the output/ directory the output of valgrind should be saved (not the query result like in test_select). The goal of the test is to look in this output from valgrind and determine if there is excessive memory leak. The oracle/ directory could contain the amount of maximum acceptable leaked bytes for each query.

Afterwards (in separate tickets) we can work to fix any memory leaks, and reduce the acceptable amounts in the oracle directory.

[Dimitar Misev]

We have this test now in testcases_manual/test_memory, and it runs test_clipping, test_nullvalues, test_select, and test_subsetting through valgrind. It's a manual test (not automatically executed on make check) for two reasons:

1. it takes a really long time to execute
2. results vary across different OS so we can't reliably set some bounds on memory issues