Fix inject_files for storing binary file.

Now a nova-api server decodes injected_files by base64 after receiving
encoded files from nova-client.
And the server fails to publish run_instance because utf8 codec can't
decode due to binary data.

This patch fixes this problem, because the base64 decode is operated when
a nova-compute server receives injected_files from a nova-api server.

Fixes bug 1112134

Change-Id: I664134c74893a970de4464161071692a5b2b5ce7
Merge "Fix inject_files for storing binary file."