[Config] Mount destinations MUST NOT be nested in Windows
[Config] Mount destinations MUST NOT be nested in Windows

This was raised during reviews with folks working on Windows Containers.  

This squashes commits from PR #433

Signed-off-by: Rob Dolin <c94deee67284244efebd7d9c5825bcff80d2bbc2@microsoft.com>
hqhq/specs,jonboulle/specs,vbatts/specs,opencontainers/specs,wking/opencontainer-runtime-spec,cloudfoundry-incubator/specs,wking/opencontainer-specs,hqhq/runtime-spec,opencontainers/runtime-spec,laijs/specs,ujuc/specs