Use tempfile.mkdtemp to avoid tempfile race

Malicious users could predict these tempfile names and overwrite root
owned files using a symlink attack.

Also fixes a bug in order of operations which caused tar to fail if
the destination directory did not exist yet.

Fixes bug #1166323

Change-Id: Ib4040eed27aa7e1e4d2bf53df6cae8e2b6c95f50
Cache metadata in /var/cache instead of /tmp

/tmp is unsafe if a user were to somehow be able to create the file
before it was cached there they can issue commands to cfn-init that
would likely elevate their permissions.

Fixes bug #1164756

Change-Id: I54e1e1be178274cb0a2b50f54e859e004e1f1c78
Remove reference to heat-api.org

Change-Id: Ida3d3f96bdbca0bf7ca81e2fb34052e7ac45598e
Prepare for release 1.2.3

Change-Id: I7a7d36b13c5b7b2683fe283f81ab2b21e4ff2359
Merge "Remove reference to heat-api.org"