qemu: set SELinux label of passt process to its own binary's label

qemu: set SELinux label of passt process to its own binary's label

set useBinarySpecificLabel = true when calling qemuSecurityCommandRun
for the passt process, so that the new process context will include
the binary-specific label that should be used for passt (passt_t)
rather than svirt_t (as would happen if useBinarySpecificLabel was
false). (The MCS part of the label, which is common to all child
processes related to a particular qemu domain instance, is also set).

Resolves: https://bugzilla.redhat.com/2172267
Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>