Make coverage tox job fail when test coverage was reduced

For the moment we can just calculate coverage and generate html with results.
It would be really useful to be able to get 'failure' by this job, when
latest commit introduced reduction of test coverage by any reason - either
addon of new code not covered with unit tests or deletion of existing unit
tests.
It will reduce total required efforts for code reviewers, that are forced now
to perform such check separately and inform about it committer.

Added file 'tools/cover.sh' is taken from OpenStack Rally project as
of state [1], with couple of fixes for satisfying 'bashate'.

Also add configuration file for coverage package.

[1] I7b4defe187c0631928d70bd09d7bcea956f4eed3

Change-Id: Ie0c5721985ae48256d9bb26af5fdb4b05797b359

.coveragerc

@@ -0,0 +1,8 @@
+[run]
+branch = True
+source = manila
+omit = manila/test*,manila/openstack/*
+
+[report]
+ignore-errors = True
+precision = 2

tools/cover.sh

@@ -0,0 +1,68 @@
+#!/bin/bash
+#
+# Copyright 2015: Mirantis Inc.
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+ALLOWED_EXTRA_MISSING=4
+TESTR_ARGS="$*"
+
+show_diff () {
+    head -1 $1
+    diff -U 0 $1 $2 | sed 1,2d
+}
+
+# Stash uncommited changes, checkout master and save coverage report
+uncommited=$(git status --porcelain | grep -v "^??")
+[[ -n $uncommited ]] && git stash > /dev/null
+git checkout HEAD^
+
+baseline_report=$(mktemp -t manila_coverageXXXXXXX)
+find . -type f -name "*.pyc" -delete && python setup.py testr --coverage --testr-args="$TESTR_ARGS"
+coverage report > $baseline_report
+baseline_missing=$(awk 'END { print $3 }' $baseline_report)
+
+# Checkout back and unstash uncommited changes (if any)
+git checkout -
+[[ -n $uncommited ]] && git stash pop > /dev/null
+
+# Generate and save coverage report
+current_report=$(mktemp -t manila_coverageXXXXXXX)
+find . -type f -name "*.pyc" -delete && python setup.py testr --coverage --testr-args="$TESTR_ARGS"
+coverage report > $current_report
+current_missing=$(awk 'END { print $3 }' $current_report)
+
+# Show coverage details
+allowed_missing=$((baseline_missing+ALLOWED_EXTRA_MISSING))
+
+echo "Allowed to introduce missing lines : ${ALLOWED_EXTRA_MISSING}"
+echo "Missing lines in master            : ${baseline_missing}"
+echo "Missing lines in proposed change   : ${current_missing}"
+
+if [ $allowed_missing -gt $current_missing ]; then
+    if [ $baseline_missing -lt $current_missing ]; then
+        show_diff $baseline_report $current_report
+        echo "I believe you can cover all your code with 100% coverage!"
+    else
+        echo "Thank you! You are awesome! Keep writing unit tests! :)"
+    fi
+    exit_code=0
+else
+    show_diff $baseline_report $current_report
+    echo "Please write more unit tests, we should keep our test coverage :( "
+    exit_code=1
+fi
+
+rm $baseline_report $current_report
+exit $exit_code

tox.ini

@@ -23,6 +23,7 @@ commands =
          contrib/ci/pre_test_hook.sh \
          contrib/ci/post_test_hook.sh \
          devstack/plugin.sh \
+         tools/cover.sh \
          run_tests.sh
 
 [testenv:genconfig]
@@ -37,9 +38,7 @@ commands = {posargs}
 commands = python setup.py build_sphinx
 
 [testenv:cover]
-commands =
-  python setup.py testr --coverage \
-    --testr-args='^(?!.*test.*coverage).*$'
+commands = {toxinidir}/tools/cover.sh {posargs}
 
 [testenv:pylint]
 deps = -r{toxinidir}/requirements.txt