[feat] put the socket in the snap folder if defined

On snap is better if we don't put stuff in /tmp but in $SNAP

src/leap/bitmask/core/__init__.py

 import platform
+import os
 
 # FIXME some temporary imports to make the modules
 # appear in the coverage report. Remove the imports when
@@ -18,6 +19,8 @@ def dummy_imports():
 APPNAME = "bitmask.core"
 if platform.system() == 'Windows':
     ENDPOINT = "tcp://127.0.0.1:5001"
+elif os.getenv('SNAP'):
+    ENDPOINT = "ipc://%s/%s.sock" % (os.getenv('SNAP'), APPNAME)
 else:
     ENDPOINT = "ipc:///tmp/%s.sock" % APPNAME