Turn off crash report if raven not available

Fix #121

gns3server/crash_report.py

@@ -15,12 +15,18 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-import raven
 import os
 import sys
 import struct
 import platform
 
+try:
+    import raven
+    RAVEN_AVAILABLE = True
+except ImportError:
+    # raven is not installed with deb package in order to simplify packagin
+    RAVEN_AVAILABLE = False
+
 from .version import __version__
 from .config import Config
 
@@ -47,6 +53,8 @@ class CrashReport:
         self._client = None
 
     def capture_exception(self, request=None):
+        if not RAVEN_AVAILABLE:
+            return
         server_config = Config.instance().get_section_config("Server")
         if server_config.getboolean("report_errors"):
             if self._client is None: