ec2 signature possible errors

[Dave Chen]

Beside the issue desribed in the bug#1289115, there are still other issues found with that piece of code, part of these issue has been confirmed with the original author.

something we need to fix:
- Check the colon from credentials['host'] instead of credentials['signature'].
- credentials['signature'] is not guaranteed to existed, so need to check it explicitly.
- Need reinitialize 'singer' to avoid contaminated status of signature.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/143772
Committed: https://git.openstack.org/cgit/openstack/keystone/commit/?id=7ace25e25fafef7809789dc3b799c1943a45301d
Submitter: Jenkins
Branch: master

commit 7ace25e25fafef7809789dc3b799c1943a45301d
Author: Dave Chen <email address hidden>
Date: Wed Dec 24 20:41:20 2014 +0800

    Fix errors in ec2 signature logic checking

    - Check for colon in credentials['host'] instead of
    credentials['signature'].
    - Fix the syntax issue when trying to get the signature
    from the dict.
    - credentials['signature'] is not guaranteed to existed,
    so check it explicitly.
    - Need to reinitialize 'signer' to avoid contaminated status
    of signature.

    Closes-Bug: #1289115
    Closes-Bug: #1434599
    Change-Id: Idb5d97c30a20872fdaafea786bcea2631d70858c