Test results with digital signature can be uploaded into Refstack.
For correct signature verification request should contain extra headers
X-Signature and X-Public-Key. Public key saves into database as metadata
to test result. Results with broken signature are ejected with HTTP error 400.
Uploading of unsigned results are not affected.
Needed-by: https://review.openstack.org/#/c/169847/
Change-Id: Ia61715a45c99e7d674f804afb0f0287ed057b1e2
a0f6974cc2