Previously dom0 had to know full path of qubes_rpc_multiplexer in VM, which can
differ between VMs (eg totally different on Windows). This commit enables dom0
to magic keyword instead of full path.
1) Instead of a set of predefined commands, we send MSG_AGENT_TO_SERVER_TRIGGER_CONNECT_EXISTING msg with a parameter (e.g. "org.qubes-os.vm.Filecopy")
defining required action
2) qrexec_daemon just forks qrexec_policy, that will take care of actually
allowing and executing required action
3) after MSG_AGENT_TO_SERVER_TRIGGER_CONNECT_EXISTING, qrexec_agent does not
execute a command - it justs uses already established file descriptors to
send data to/from. Thus, there is no need to use ~/.xxxxxspool - a command line
tool can have direct access to remote fds.
After yum transaction (install/upgrade/remove),
yum-plugin-post-transaction-actions will execute script which trigger
qvm-sync-appmenus in dom0 (through qrexec).
THIS INTRODUCE NEW PREDEFINED COMMAND IN QREXEC
Processes in AppVM can ask qrexec-agent to send a
MSG_AGENT_TO_SERVER_TRIGGER_EXEC message to qrexec-daemon.
The latter will execute predefined program. It is useful for
the purpose of file copy; the predefined program will create
a connected qfile-daemon<->qfile-agent pair.
