[__line/state] Make sure the index match is at the beginning

Without the == 1 all lines which contain --line as a substring match.  e.g. if
--line is "line" and the file contains the line "wrong line" this was considered
a match.

cdist/conf/type/__line/explorer/state

@@ -49,7 +49,7 @@ function _find(_text, _pattern) {
    if (needle == "regex") {
       return match(_text, _pattern)
    } else {
-      return index(_text, _pattern)
+      return index(_text, _pattern) == 1
    }
 }
 BEGIN {