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

[thopre]

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.

[PrzemekWirkus]

LGTM

[thopre]

Committed as ed0c7da16e11d6e6e5757117594fc18c041a1b95

lnt/server/db/testsuitedb.py

def _importSampleValues(self, session, tests_data, run, config):
                 session.add(test)
 
             samples = []
             for key, values in test_data.items():
                 if key == 'name' or key == "id" or key.endswith("_id"):
                     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):
                     values = [values]
                 while len(samples) < len(values):
                     sample = self.Sample(run, test)
                     samples.append(sample)
                     all_samples_to_add.append(sample)

tests/server/db/yamlschema.shtest

 # CHECK: PASS : 3
 
 
 # Migration Tests
 # ===============
 #
 # 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"
 # RUN: ln -sf "%S/Inputs/schema-example-nomigration0.yaml" "%t.install/schemas/my_suite.yaml"
 # RUN: not lnt import "%t.install" -s my_suite "%S/Inputs/customschema-report.json" 2>&1 | FileCheck %s --check-prefix=NOMIGRATION0
 # NOMIGRATION0: Cannot automatically migrate database: Metrics removed: data_size
 #
 # RUN: rm -f "%t.install/schemas/my_suite.yaml"