Skip nodes functionality for Package and Network modules

Added to main entrypoint
- Skip nodes using simple argument with '*' as a trailing wildcard
- Skip nodes using file list

Usability improovement
- Node list preview in status line
- Node stats alignment in net report

Minor fixes:
- Python version detection (3.5+)
- Node counter for each status
- Proper node skip handling

Change-Id: I086ef501bc06f0e739df25349257f1c63a2e2fcf
Related-PROD: PROD-35009
diff --git a/cfg_checker/modules/network/pinger.py b/cfg_checker/modules/network/pinger.py
index 0500284..5b12a94 100644
--- a/cfg_checker/modules/network/pinger.py
+++ b/cfg_checker/modules/network/pinger.py
@@ -10,10 +10,21 @@
 
 # This is independent class with a salt.nodes input
 class NetworkPinger(object):
-    def __init__(self, mtu=None, detailed=False, errors_class=None):
+    def __init__(
+        self,
+        mtu=None,
+        detailed=False,
+        errors_class=None,
+        skip_list=None,
+        skip_list_file=None
+    ):
         logger_cli.info("# Initializing")
         # all active nodes in the cloud
-        self.target_nodes = salt_master.get_nodes()
+        self.target_nodes = salt_master.get_nodes(
+            skip_list=skip_list,
+            skip_list_file=skip_list_file
+        )
+
         # default MTU value
         self.target_mtu = mtu if mtu else 64
         # only data