Create new virtmgr binary from virtualizationservice

To bootstrap separation of virtualizationservice into two binaries
(global service and user instance), start by compiling a second binary
out of the same source code, just using a diffrent main source file.

The new binary has a command line interface that takes two file
descriptors - a socketpair() fd to start RpcBinder server on, and
a pipe() fd to use for signalling when the server has been started.

The process registers a death notification to kill itself when the
parent process has died.

Bug: 245727626
Test: builds, not used in tests yet
Change-Id: I0c4c7892af91b6deb5ece60e0d1b49a2b4356d35