SizeRW & SizeRootFs omitted if empty in /container/json call
SizeRW & SizeRootFs omitted if empty in /container/json call

Signed-off-by: Antonio Murdaca <f9809039ea4850e75dcb8d80b778844aa463358f@linux.com>

vdemeester/engine-api,jwhonce/engine-api,thaJeztah/engine-api,mikedougherty/engine-api,docker/engine-api,msabansal/engine-api,rhatdan/engine-api