cleanup pyc files between running pytest

this is need to avoid problem sometimes tests are run inside docker
container and sometimes local.

Traceback (most recent call last):
File "/usr/lib/python2.7/dist-packages/_pytest/config/__init__.py", line 409, in _importconftest
mod = conftestpath.pyimport()
File "/usr/lib/python2.7/dist-packages/py/_path/local.py", line 686, in pyimport
raise self.ImportMismatchError(modname, modfile, self)
ImportMismatchError: ('conftest', '/beremiz/tests/tools/conftest.py', local('/home/developer/beremiz/tests/tools/conftest.py'))
ERROR: could not load /home/developer/beremiz/tests/tools/conftest.py

--- a/tests/tools/run_python_tests.sh	Thu Oct 04 17:24:40 2018 +0300
+++ b/tests/tools/run_python_tests.sh	Fri Oct 05 13:11:28 2018 +0300
@@ -1,17 +1,28 @@
 #!/bin/sh
 
+cleanup()
+{
+    find ./tests/tools -name '*.pyc' -delete
+}
+
 LC_ALL=ru_RU.utf-8
 
 export DISPLAY=:42
 Xvfb $DISPLAY -screen 0 1280x1024x24 &
 sleep 1
 
+
+cleanup
+
 ret=0
 DELAY=400
 KILL_DELAY=$(($DELAY + 30))
 timeout -k $KILL_DELAY $DELAY pytest --timeout=10 ./tests/tools
 ret=$?
 
+cleanup
+
+
 pkill -9 Xvfb
 
 exit $ret