Move haskell test code to htest/

This is the first commit of a series that will attempt to cleanup the
test code organisation, which evolved somewhat organically from the
initial pure htools functionality.

The proposed organisation of the tree will be as follows:

- htools (or maybe renamed to haskell or hs): only production code
- htest: top-level test directory, containing test.hs, static helper
  scripts, etc.
- htest/Ganeti/*.hs: modules implementing the actual test properties
  and test cases for the correspondingly-named production code modules
- htest/data: containing test data files for the test cases

This particular patch moves all the test code (test.hs, hpc-htools.hs
symlink) and helper scripts (offline-test.sh, etc.) from htools/ to
htest/, while updating the files themselves (if they had paths
mentioning htools/), .gitignore and the Makefile.

The only special mention is that in Makefile, we used to have a BINARY
shell variable in binary build rule; that was computed via stripping
`htools/' prefix; I've cleaned that and replaced with $(notdir $@);
even though it's duplicated a few times, it leads to more readable
make output (and easier to copy-paste).

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Agata Murawska <agatamurawska@google.com>