saml: populate fingerprints from all signing keys in metadata
saml: populate fingerprints from all signing keys in metadata

Change-Id: I7daa3f69352fb27d0386a3468d61455f2331e48d
Reviewed-on: https://gerrit.instructure.com/154834
Tested-by: Jenkins
Reviewed-by: Carl Kibler <7c2b40129dd885a147d5b2dda56dda016b9a8f57@instructure.com>
Reviewed-by: Brent Burgoyne <bccf16d7abdd2611580b1cd7d7a6fcc150d619da@instructure.com>
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

instructure/canvas-lms,djbender/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,sfu/canvas-lms,djbender/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,instructure/canvas-lms,sfu/canvas-lms