Adjust disallowed CpuShares in /containers/create

Previous versions of libcontainer allowed CpuShares that were greater
than the maximum or less than the minimum supported by the kernel, and
relied on the kernel to do the right thing. Newer libcontainer fails
after creating the container if the requested CpuShares is different
from what was actually created by the kernel, which breaks compatibility
with earlier Docker Remote API versions. This change explicitly adjusts
the requested CpuShares in API versions < 1.20.

Signed-off-by: Samuel Karp <skarp@amazon.com>
(cherry picked from commit ed39fbeb2a)

api/server/server.go

@@ -903,6 +903,7 @@ func (s *Server) postContainersCreate(version version.Version, w http.ResponseWr
 	if err != nil {
 		return err
 	}
+	adjustCpuShares(version, hostConfig)
 
 	containerId, warnings, err := s.daemon.ContainerCreate(name, config, hostConfig)
 	if err != nil {