control: Add (build) dependency on mount

mount is no longer essential, so we need to explicitly depend
on it.

We should be able to drop the build dependency later, after
patching out the check upstream, but the runtime dependency is
here to stay.

Closes: #1023420

debian/control

@@ -50,6 +50,7 @@ Build-Depends:
  libyajl-dev,
  lvm2 [linux-any],
  meson,
+ mount,
  nfs-common:native,
  numad:native [linux-any],
  open-iscsi [linux-any],
@@ -126,6 +127,7 @@ Recommends:
  libvirt-daemon-driver-xen (= ${binary:Version}),
  libxml2-utils,
  lvm2 [linux-any],
+ mount,
  netcat-openbsd,
  qemu-kvm | qemu-system,
 Suggests: