Add master flag `--filter-gpu-resources={true|false}`

Per the email thread below, we are adding a new flag on the master called --filter-gpu-resources to enable / disable honoring the GPU_RESOURCES framework capability.

https://www.mail-archive.com/dev@mesos.apache.org/msg37571.html

When set to true, this flag will cause the mesos master to continue to
function as it does today. That is, it will filter offers containing GPU
resources and only send them to frameworks that opt into the GPU_RESOURCES framework capability. When set to false, this flag will cause the master to not filter offers containing GPU resources, and indiscriminately send them to all frameworks whether they set the GPU_RESOURCES capability or not.

This is a temporary flag that will eventually be removed. We will remove it once we have better support for achieving the same functionality that the GPU_RESOURCES capability gives you.

As described in the email, this support relies on dynamic reservations, hierarchical roles, and support for reservations to multiple roles (an unyet implemented feature). The JIRA tracking these features are linked below.