erasure-code: Backward compatibility with legacy EC plugins

erasure-code: Backward compatibility with legacy EC plugins

Resurrected jerasure_generic, jerasure_sse3, jerasure_sse4, jerasure_neon,
shec_generic, shec_sse3, shec_sse4 and shec_neon. These all are exact
copies of the new jerasure and shec plugins that support SIMD detection.

Moved EC preload code in ceph-mon and ceph-osd to a central location, added
warning when preloading legacy plugins.

OSMonitor::get_erasure_code and OSDMonitor:normalize_profile will now check
if legacy EC plugins are used and log a warning.

Added tests to check that warnings make it to the log.

Signed-off-by: Bassam Tabbara <bassam.tabbara@quantum.com>