lttng-tools: add systemd support

Add systemd service file of lttng-tools from Fedora

ftp://fr2.rpmfind.net/linux/fedora/linux/development/rawhide
/Everything/source/tree/Packages/l/lttng-tools-2.10.5-1.fc29.src.rpm

It requires kernel configs CONFIG_STAGING and CONFIG_LTTNG2 to be set.
But linux-yocto doesn't meet the requirement. So disable the service by
default.

(From OE-Core rev: 29bc046d705beb9dac2e70fa31358da7719ba7a4)

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-kernel/lttng/lttng-tools/lttng-sessiond.service

@@ -0,0 +1,9 @@
+[Unit]
+Description=LTTng 2.x central tracing registry session daemon
+
+[Service]
+Type=forking
+ExecStart=/usr/bin/lttng-sessiond -d
+
+[Install]
+WantedBy=multi-user.target

meta/recipes-kernel/lttng/lttng-tools_2.9.5.bb

@@ -31,12 +31,16 @@ SRC_URI = "https://lttng.org/files/lttng-tools/lttng-tools-${PV}.tar.bz2 \
            file://x32.patch \
            file://run-ptest \
            file://0001-Allow-multiple-attempts-to-connect-to-relayd.patch \
+           file://lttng-sessiond.service \
            "
 
 SRC_URI[md5sum] = "051224eb991aee07f8721ff1877d0b96"
 SRC_URI[sha256sum] = "77839eb6fc6c652125f08acfd9369701c2516eb05cc2084160e7efc7a3fb731c"
 
-inherit autotools ptest pkgconfig useradd python3-dir manpages
+inherit autotools ptest pkgconfig useradd python3-dir manpages systemd
+
+SYSTEMD_SERVICE_${PN} = "lttng-sessiond.service"
+SYSTEMD_AUTO_ENABLE = "disable"
 
 USERADD_PACKAGES = "${PN}"
 GROUPADD_PARAM_${PN} = "tracing"
@@ -52,6 +56,12 @@ FILES_${PN}-dev += "${PYTHON_SITEPACKAGES_DIR}/*.la"
 INSANE_SKIP_${PN} = "libexec dev-so"
 INSANE_SKIP_${PN}-dbg = "libexec"
 
+do_install_append () {
+    # install systemd unit file
+    install -d ${D}${systemd_unitdir}/system
+    install -m 0644 ${WORKDIR}/lttng-sessiond.service ${D}${systemd_unitdir}/system
+}
+
 do_install_ptest () {
     for f in Makefile tests/Makefile tests/utils/utils.sh ; do
         install -D "${B}/$f" "${D}${PTEST_PATH}/$f"