Improve logging for template syntax errors

The shlex splitting can fail, resulting in error messages like:

ERROR livemedia-creator: No closing quotation

without any context in the log files. This logs the line that failed to
be split and expanded.

(cherry picked from commit f9665940bb)
(cherry picked from commit 4c0e632b93)

src/pylorax/ltmpl.py

@@ -67,10 +67,16 @@ class LoraxTemplate(object):
         # remove comments
         lines = [line for line in lines if not line.startswith("#")]
 
-        # split with shlex and perform brace expansion
-        lines = [split_and_expand(line) for line in lines]
-
-        return lines
+        # split with shlex and perform brace expansion. This can fail, so we unroll the loop
+        # for better error reporting.
+        expanded_lines = []
+        try:
+            for line in lines:
+                expanded_lines.append(split_and_expand(line))
+        except Exception as e:
+            logger.error('shlex error processing "%s": %s', line, str(e))
+            raise
+        return expanded_lines
 
 def split_and_expand(line):
     return [exp for word in shlex.split(line) for exp in brace_expand(word)]