netlink: force python to load ifupdown2's nlmanager cpy instead of python-nlmanager

Ticket: CM-13453
Reviewed By: Roopa, Nikhil G, Daniel W
Testing Done: ifupdown2-tests

We had an issue where python-nlmanager and ifupdown2's nlmanager differed
When netd starts it loads ifupdown2's addons, so it also tries to do the
imports. Since the current working directy is not /usr/share/ifupdown2 but
netd directory it won't load ifupdown2's nlmanager first but python-nlmanager
if it exists.

Here we insert/hardcode /usr/share/ifupdown2/ first in the path to make sure
we load the right nlmanager

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>

ifupdown/netlink.py

@@ -6,7 +6,6 @@
 
 try:
     from ifupdownaddons.utilsbase import utilsBase
-    from nlmanager.nlmanager import NetlinkManager
     import ifupdown.ifupdownflags as ifupdownflags
 except ImportError, e:
     raise ImportError(str(e) + "- required module not found")
@@ -17,7 +16,16 @@ class Netlink(utilsBase):
 
     def __init__(self, *args, **kargs):
         utilsBase.__init__(self, *args, **kargs)
-        self._nlmanager_api = NetlinkManager(extra_debug=False)
+        try:
+            import sys
+            sys.path.insert(0, '/usr/share/ifupdown2/')
+            from nlmanager.nlmanager import NetlinkManager
+            # this should force the use of the local nlmanager
+            self._nlmanager_api = NetlinkManager(extra_debug=False)
+        except Exception as e:
+            self.logger.error('cannot initialize ifupdown2\'s '
+                              'netlink manager: %s' % str(e))
+            raise
 
     def get_iface_index(self, ifacename):
         if ifupdownflags.flags.DRYRUN: return