Handle blank lines followed by comment in nic conversion script

Currently if a blank line is followed by a comment the 'last_non_comment_spaces'
variable gets reset, which results in the comment line not being indented.
This just ignores blank lines so that 'last_non_comment_spaces' isn't reset
and the comment line is properly indented.

Closes-Bug: 1779191
Change-Id: I286da578c42df24242ba38df12d42c8a8fdd4a4f

releasenotes/notes/nic-config-script-handle-blank-line-f86553d7589826ed.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - This fixes an issue with the yaml-nic-config-2-script.py script
+    that converts old-style nic config files to new-style. It now handles
+    blank lines followed by a comment line.

tools/yaml-nic-config-2-script.py

@@ -49,6 +49,9 @@ def to_commented_yaml(filename):
     with open(filename, 'r') as f:
         comment_count = 0
         for line in f:
+            # skip blank line
+            if line.isspace():
+                continue;
             char_count = 0
             spaces = ''
             for char in line: