Rules: comments-indentation: Allow two levels

Previously only comments that were indented like the following content
line were allowed, e.g.:

    prev: line:
      # commented line
      current: line

With this change, such new cases are also allowed:

      prev: line
      # commented line 1
    # commented line 2
    current: line

yamllint/rules/comments_indentation.py

@@ -17,27 +17,48 @@
 import yaml
 
 from yamllint.errors import LintProblem
-from yamllint.rules.common import get_comments_between_tokens
+from yamllint.rules.common import get_line_indent, get_comments_between_tokens
 
 
 ID = 'comments-indentation'
 TYPE = 'token'
 
 
+# Case A:
+#
+#     prev: line:
+#       # commented line
+#       current: line
+#
+# Case B:
+#
+#       prev: line
+#       # commented line 1
+#     # commented line 2
+#     current: line
+
 def check(conf, token, prev, next):
     if prev is None:
         return
 
-    token_indent = token.start_mark.column
+    curr_line_indent = token.start_mark.column
     if isinstance(token, yaml.StreamEndToken):
-        token_indent = 0
+        curr_line_indent = 0
 
-    skip_first = True
+    skip_first_line = True
     if isinstance(prev, yaml.StreamStartToken):
-        skip_first = False
+        skip_first_line = False
+        prev_line_indent = 0
+    else:
+        prev_line_indent = get_line_indent(prev)
 
-    for comment in get_comments_between_tokens(prev, token,
-                                               skip_first_line=skip_first):
-        if comment.column != token_indent + 1:
+    if prev_line_indent <= curr_line_indent:
+        prev_line_indent = -1  # disable it
+
+    for comment in get_comments_between_tokens(
+            prev, token, skip_first_line=skip_first_line):
+        if comment.column - 1 == curr_line_indent:
+            prev_line_indent = -1  # disable it
+        elif comment.column - 1 != prev_line_indent:
             yield LintProblem(comment.line, comment.column,
                               'comment not indented like content')

yamllint/rules/common.py

@@ -64,6 +64,16 @@ class Comment(object):
                 str(self) == str(other))
 
 
+def get_line_indent(token):
+    """Finds the indent of the line the token starts in."""
+    start = token.start_mark.buffer.rfind('\n', 0,
+                                          token.start_mark.pointer) + 1
+    content = start
+    while token.start_mark.buffer[content] == ' ':
+        content += 1
+    return content - start
+
+
 def get_comments_between_tokens(token1, token2, skip_first_line=False):
     if token2 is None:
         buf = token1.end_mark.buffer[token1.end_mark.pointer:]