UBUNTU: [Packaging] Add systemd service to load intel_sgx

BugLink: https://bugs.launchpad.net/bugs/1844245

Include a systemd service to simplify the process of loading intel_sgx
during the boot if the user decides to do so.

Since intel_sgx will only be available in linux-azure, restrict the
new service with ConditionVirtualization=microsoft.
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
Acked-by: Connor Kuehl <connor.kuehl@canonical.com>
Acked-by: Andy Whitcroft <andy.whitcroft@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
[ Connor Kuehl: dh_installinit on Xenial does not have the --no-enable
  switch, so I've removed that switch from this patch for Xenial. ]
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>

debian/linux-cloud-tools-common.intel-sgx-load-module.service

+[Unit]
+Description=Install SGX kernel module
+DefaultDependencies=false
+ConditionVirtualization=microsoft
+
+[Service]
+Type=oneshot
+RemainAfterExit=true
+ExecStart=/sbin/modprobe intel_sgx
+ExecStop=/sbin/modprobe -r intel_sgx
+
+[Install]
+WantedBy=multi-user.target

debian/rules.d/3-binary-indep.mk

@@ -206,6 +206,9 @@ ifeq ($(do_tools_hyperv),true)
 	dh_installinit -p$(cloudpkg) -o --name hv-fcopy-daemon
 	dh_systemd_start -p$(cloudpkg)
 endif
+	# Keep intel_sgx service disabled by default, so add it after dh_systemd_enable
+	# and dh_systemd_start are called:
+	dh_installinit -p$(cloudpkg) --no-start --name intel-sgx-load-module
 endif
 endif
 	dh_installdeb -i