[CRIU] Inherit FD via RPC

[Adrian Reber]

Hello Andrei,

this is my next try to get inherit-fd support into RPC.

For each inherit-fd a new notify message ('request-inherit-fd') is sent to
the RPC client, which then transmits the actual FD back to CRIU.

I have this working in combination with runc and I am just sending this
out if this is how you described it.

I have not waited for the travis results but just wanted to get some
feedback from you. Let me know if you think this is the right way to
go.

I still would change the commit messages to have more details and
fix errors if travis or jenkins complains.

		Adrian