Report txt: fix printing of non-ascii details (#844)

Previous commit introduced couple of issues regarding details of
reports that could lead to situations like:
* remediation instructions has not been printed when non-ascii
  characters have been present
* possible unwanted empty line when remediation has been specified
  but relative symlinks hasn't
* if the URL title contained non-ascii character, it has been broken
  too (on py2)

This should handle all mentioned problems when generating the txt
file.

leapp/utils/report.py

@@ -116,27 +116,38 @@ def importance(message):
     return SEVERITY_LEVELS.get(message['severity'], 99)
 
 
+def _treat_str(text):
+    """
+    Ensure the given text is decoded.
+
+    This is problem in case of Py2 when non-asci characters are present.
+    """
+    return text.decode('utf-8') if isinstance(text, six.binary_type) else text
+
+
 def _report_detail_to_string(report_detail):
     detail = u''
     external_links = report_detail[ExternalLink.name] if ExternalLink.name in report_detail.keys() else None
     remediation = Remediation.from_dict(report_detail)
 
     if external_links:
-        external_links_text = u'Related links:'
+        external_links_text = u'Related links:\n'
         for link in external_links:
-            external_links_text += u'\n    - {}: {}'.format(link['title'], link['url'])
+            # Note(pstodulk): IRI could contain unicode characters. Even when it's
+            # still unexpected , let's reather treat it as well.
+            external_links_text += u'    - {}: {}\n'.format(
+                _treat_str(link['title']),
+                _treat_str(link['url'])
+            )
         detail += external_links_text
 
     if remediation:
         # NOTE(ivasilev) Decoding is necessary in case of python2 as remediation is an encoded string,
         # while io.open expects "true text" input. For python3 repr will return proper py3 str, no
         # decoding will be needed.
         # This hassle and clumsiness makes me sad, so suggestions are welcome.
-        remediation_text = '\nRemediation: {}\n'.format(remediation)
-        if isinstance(remediation_text, six.binary_type):
-            # This will be true for py2 where repr returns an encoded string
-            remediation_text = remediation_text.decode('utf-8')
-            detail += remediation_text
+        remediation_text = 'Remediation: {}\n'.format(remediation)
+        detail += _treat_str(remediation_text)
 
     return detail
 
@@ -156,8 +167,7 @@ def generate_report_file(messages_to_report, context, path, report_schema='1.1.0
                 f.write(u'Risk Factor: {} {}\n'.format(message['severity'], flag))
                 f.write(u'Title: {}\n'.format(message['title']))
                 f.write(u'Summary: {}\n'.format(message['summary']))
-                report_detail = message.get('detail', {})
-                detail = _report_detail_to_string(report_detail)
+                detail = _report_detail_to_string(message.get('detail', {}))
                 f.write(detail)
                 if report_schema_tuple > (1, 0, 0):
                     # report-schema 1.0.0 doesn't have a stable report key