Bug fix: abort on fatal initialization errors

* The netsim initialization module failed to abort after reporting
  incorrect python-box version because sys.exit was executed
  inside the try block
* Netlab reported a failure to import netsim but then tried to
  continue like nothing happened

netlab

@@ -2,11 +2,13 @@
 #
 # Main netsim-tools CLI command
 #
+import sys
 
 try:
   import netsim
   import netsim.cli
 except:
   print("Cannot import netsim Python module, netlab installation is broken")
+  sys.exit(1)
 
 netsim.cli.lab_commands(__file__)

netsim/__init__.py

@@ -4,11 +4,17 @@
 
 __version__ = "1.9.2-dev1"
 
+abort = False
+
 try:
   import box
 
   if box.__version__ < '7.2.0':                 # netlab needs Python Box version 7.0 or higher
     print("FATAL ERROR: python-box version 7.2.0 or higher required, use 'pip3 install --upgrade python-box' to install")
-    sys.exit(1)
+    abort = True
+
 except:                                       # box is not installed, something else is bound to fail ;)
   pass
+
+if abort:
+  sys.exit(1)