Consider updating name for envvar THREESCALE_SANDBOX_PROXY_OPENSSL_VERIFY_MODE

As observed in issue https://issues.jboss.org/browse/THREESCALE-1429, currently the environment variable THREESCALE_SANDBOX_PROXY_OPENSSL_VERIFY_MODE exists, and the nomenclature of "sandbox" has been updated to "staging".

This does not break anything, but conceptually might make sense to update the value for example to THREESCALE_STAGING_PROXY_OPENSSL_VERIFY_MODE. If that's the case then system would have to update the code first to take into account the new environment variable name, and then the templates should be updated to use the new name. Take into account that updating the variable name would require an upgrade process unless the old existing name is keep compatible too.

This will not be changed for 2.4. I leave it to product team to prioritize this in the future.