[LNT] Python 3 support: print unknown metric with str

Summary:
When encountering an unknown metric, LNT throws a ValueError with a
message indicating the problem. That message uses %r and thus `__repr__`
to print the metric name which leads to difference between Python 2 and
Python 3 since the former prefix unicode string with a 'u' but the
latter do not. This leads to a failure of server/db/yamlschema.shtest.

This commit uses %s and thus `__str__` to get a consistent display and
adapt the test accordingly.

Reviewers: cmatthews, hubert.reinterpretcast, kristof.beyls, leandron, PrzemekWirkus

Reviewed By: PrzemekWirkus

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D68801

Author: Thomas Preud'homme

lnt/server/db/testsuitedb.py

@@ -1054,7 +1054,7 @@ def _importSampleValues(self, session, tests_data, run, config):
                     continue
                 field = field_dict.get(key)
                 if field is None and key != 'profile':
-                    raise ValueError("test %r: Metric %r unknown in suite " %
+                    raise ValueError("test %s: Metric '%s' unknown in suite " %
                                      (name, key))
 
                 if not isinstance(values, list):

tests/server/db/yamlschema.shtest

@@ -20,7 +20,7 @@
 #
 # Inserting with an extra field shouldn't work just yet
 # RUN: not lnt import "%t.install" -s my_suite "%S/Inputs/customschema-report2.json" 2>&1 | FileCheck %s --check-prefix=NOTUPGRADED
-# NOTUPGRADED: Metric u'newfield' unknown in suite
+# NOTUPGRADED: Metric 'newfield' unknown in suite
 
 # Upgrading to a schema with metrics/fields removed should fail
 # RUN: rm -f "%t.install/schemas/my_suite.yaml"