Unit tests fail without hylaa, spaceex, flowstar

[MaxGaukler]

ant test fails without Hylaa, SpaceEx and Flowstar installed, whereas other missing tools are gracefully ignored.

     [exec] Using 4 parallel processes.
     [exec] 0/96 Running mcs_8 with flowstar and timeout 2.0
     [exec] 1/96 Running mcs_8 with hylaa and timeout 2.0
     [exec] 2/96 Running mcs_8 with dreach and timeout 2.0
     [exec] 3/96 Running mcs_8 with spaceex and timeout 2.0
     [exec] Traceback (most recent call last):
     [exec]   File "/hyst/src/hybridpy/hybridpy/tool_hylaa.py", line 71, in <module>
     [exec]     tool_main(HylaaTool())
     [exec]   File "/hyst/src/hybridpy/hybridpy/hybrid_tool.py", line 76, in tool_main
     [exec]     code = tool_obj.run()
     [exec]   File "/hyst/src/hybridpy/hybridpy/hybrid_tool.py", line 302, in run
     [exec]     rv = self._run_tool(image_requested)
     [exec]   File "/hyst/src/hybridpy/hybridpy/tool_hylaa.py", line 28, in _run_tool
     [exec]     loaded_module = imp.load_source(mod_name, filepath)
     [exec]   File "/tmp/pysim_725_2412717/mcs_8_hylaa.py", line 9, in <module>
     [exec] ImportError: No module named hylaa.hybrid_automaton
     [exec] 0/96 Finished mcs_8 with flowstar
     [exec] 4/96 Running mcs_8 with hycreate and timeout 2.0
     [exec] 2/96 Finished mcs_8 with dreach
     [exec] 5/96 Running mcs_8 with pysim and timeout 2.0
     [exec] Test failed for 1/96 model mcs_8 with hylaa: Error (Tool)
     [exec] 
     [exec] Log:
     [exec] Running Hyst...
     [exec] Using Hyst to convert model '/hyst/src/tests/integration/models/8d_motor/mcs_8.xml' for hylaa.
     [exec] Hyst command: java -jar /hyst/src/Hyst.jar -i /hyst/src/tests/integration/models/8d_motor/mcs_8.xml -o /hyst/src/tests/integration/result/mcs_8_hylaa.py -tool hylaa ''
     [exec] Seconds for Hyst conversion: 3.4865219593
     [exec] Hypy Elapsed Seconds: 3.67423415184
     [exec] Hypy Result: Error (Tool)
     [exec] 
     [exec] 
     [exec] Error detected running integration tests.
     [exec] 3/96 Finished mcs_8 with spaceex
     [exec] 4/96 Finished mcs_8 with hycreate
     [exec] 5/96 Finished mcs_8 with pysim

BUILD FAILED
/hyst/src/build.xml:211: exec returned: 1