remove quickcheck from the testdependencies

it spilled a warning about not being build for java 7
added tests for crate signal handling
fix tracking of active sql requests
upgrade crate-python used for tests to 0.12.0

in order to use the improved CrateLayer
Merge pull request #1178 from crate/m/process_tests

M/process tests
renamed NullType to UndefinedType in order to avoid confusion