Add tool to migrate files from tempest into lib

This commit adds a new tool to migrate files with history into
tempest-lib. When migrating functionality into tempest we need to
use this instead of copying and pasting files so that we preserve the
commit history from tempest.

tools/migrate_from_tempest.sh

@@ -0,0 +1,116 @@
+#!/bin/bash
+#
+# Use this script to move over a set of files from tempest master with commit
+# history into the tempest lib. You must only do this for files that haven't
+# been migrated over already.
+# 
+# To use:
+#  1. Create a new branch in the tempest-lib repo so not to destroy your current
+#     working branch
+#  2. Run the script from the repo dir and specify the file paths relative to
+#     the root tempest dir(only code and unit tests):
+#
+#   tools/migrate_from_tempest.sh tempest/
+
+
+function usage {
+    echo "Usage: $0 [OPTION] file1 file2"
+    echo "Migrate files from tempest"
+    echo ""
+    echo "-o, --output_dir      Specify an directory relative to the repo root to move the migrated files into."
+}
+
+set -e
+
+output_dir=""
+
+while [ $# -gt 0 ]; do
+    case "$1" in
+        -h|--help) usage; exit;;
+        -o|--output_dir) output_dir="$2"; shift;;
+        *) files="$files $1";;
+    esac
+    shift
+done
+
+TEMPEST_GIT_URL=git://git.openstack.org/openstack/tempest
+
+tmpdir=$(mktemp -d -t tempest-migrate.XXXX)
+tempest_lib_dir=$(dirname "$0")
+
+function count_commits {
+    echo
+    echo "Have $(git log --oneline | wc -l) commits"
+}
+
+# Clone tempest and cd into it
+git clone $TEMPEST_GIT_URL $tmpdir
+cd $tmpdir
+
+# Build the grep pattern for ignoring files that we want to keep
+keep_pattern="\($(echo $files | sed -e 's/ /\\|/g')\)"
+# Prune all other files in every commit
+pruner="git ls-files | grep -v \"$keep_pattern\" | git update-index --force-remove --stdin; git ls-files > /dev/stderr"
+
+# Find all first commits with listed files and find a subset of them that
+# predates all others
+roots=""
+for file in $files; do
+    file_root="$(git rev-list --reverse HEAD -- $file | head -n1)"
+    fail=0
+    for root in $roots; do
+         if git merge-base --is-ancestor $root $file_root; then
+             fail=1
+             break
+         elif !git merge-base --is-ancestor $file_root $root; then
+             new_roots="$new_roots $root"
+         fi
+     done
+     if [ $fail -ne 1 ]; then
+         roots="$new_roots $file_root"
+     fi
+done
+
+set_roots="
+if [ '' $(for root in $roots; do echo " -o \"\$GIT_COMMIT\" == '$root' "; done) ]; then
+    echo ''
+else
+    cat
+fi"
+
+# Enhance git_commit_non_empty_tree to skip merges with:
+# a) either two equal parents (commit that was about to land got purged as well
+# as all commits on mainline);
+# b) or with second parent being an ancestor to the first one (just as with a)
+# but when there are some commits on mainline).
+# In both cases drop second parent and let git_commit_non_empty_tree to decide
+# if commit worth doing (most likely not).
+
+skip_empty=$(cat << \EOF
+if [ $# = 5 ] && git merge-base --is-ancestor $5 $3; then
+    git_commit_non_empty_tree $1 -p $3
+else
+    git_commit_non_empty_tree "$@"
+fi
+EOF
+)
+
+git filter-branch --index-filter "$pruner" --parent-filter "$set_roots" --commit-filter "$skip_empty" HEAD
+
+# Pull changes
+cd -
+git remote add tempest-migrate $tmpdir
+git pull tempest-migrate master
+git remote rm tempest-migrate
+
+for file in $files; do
+    filename=`basename $file`
+    if [ -n "$output_dir" ]; then
+        git mv $file "$output_dir/$filename"
+    else
+        git mv $file "tempest_lib/$filename"
+    fi
+done
+rm -r tempest
+git add .
+git commit -m "Moved files from previous merge as part of tempest migration"