systemd: do not rely on racy heuristics to determine master PID

This fixes reloads and stops when systemd is unable to guess master process PID
due to a race described in https://trac.nginx.org/nginx/ticket/1897

While we wait for a proper fix is introduced in either nginx or systemd via
Type=forking, the workaround is not to rely on possibly unset variables, but
hardcode the path to PID file instead where we need it.

debian/nginx-debug.service

diff --git a/debian/nginx-debug.service b/debian/nginx-debug.service
index 142d2a6..af0bba4 100644
--- a/debian/nginx-debug.service
+++ b/debian/nginx-debug.service
@@ -8,8 +8,8 @@
 Type=forking
 PIDFile=/var/run/nginx.pid
 ExecStart=/usr/sbin/nginx-debug -c /etc/nginx/nginx.conf
-ExecReload=/bin/kill -s HUP $MAINPID
-ExecStop=/bin/kill -s TERM $MAINPID
+ExecReload=/bin/sh -c "/bin/kill -s HUP $(/bin/cat /var/run/nginx.pid)"
+ExecStop=/bin/sh -c "/bin/kill -s TERM $(/bin/cat /var/run/nginx.pid)"
 
 [Install]
 WantedBy=multi-user.target

debian/nginx.service

diff --git a/debian/nginx.service b/debian/nginx.service
index 23eb0ed..e509a2e 100644
--- a/debian/nginx.service
+++ b/debian/nginx.service
@@ -8,8 +8,8 @@
 Type=forking
 PIDFile=/var/run/nginx.pid
 ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.conf
-ExecReload=/bin/kill -s HUP $MAINPID
-ExecStop=/bin/kill -s TERM $MAINPID
+ExecReload=/bin/sh -c "/bin/kill -s HUP $(/bin/cat /var/run/nginx.pid)"
+ExecStop=/bin/sh -c "/bin/kill -s TERM $(/bin/cat /var/run/nginx.pid)"
 
 [Install]
 WantedBy=multi-user.target

rpm/SOURCES/nginx-debug.service

diff --git a/rpm/SOURCES/nginx-debug.service b/rpm/SOURCES/nginx-debug.service
index 142d2a6..af0bba4 100644
--- a/rpm/SOURCES/nginx-debug.service
+++ b/rpm/SOURCES/nginx-debug.service
@@ -8,8 +8,8 @@
 Type=forking
 PIDFile=/var/run/nginx.pid
 ExecStart=/usr/sbin/nginx-debug -c /etc/nginx/nginx.conf
-ExecReload=/bin/kill -s HUP $MAINPID
-ExecStop=/bin/kill -s TERM $MAINPID
+ExecReload=/bin/sh -c "/bin/kill -s HUP $(/bin/cat /var/run/nginx.pid)"
+ExecStop=/bin/sh -c "/bin/kill -s TERM $(/bin/cat /var/run/nginx.pid)"
 
 [Install]
 WantedBy=multi-user.target

rpm/SOURCES/nginx.service

diff --git a/rpm/SOURCES/nginx.service b/rpm/SOURCES/nginx.service
index 23eb0ed..e509a2e 100644
--- a/rpm/SOURCES/nginx.service
+++ b/rpm/SOURCES/nginx.service
@@ -8,8 +8,8 @@
 Type=forking
 PIDFile=/var/run/nginx.pid
 ExecStart=/usr/sbin/nginx -c /etc/nginx/nginx.conf
-ExecReload=/bin/kill -s HUP $MAINPID
-ExecStop=/bin/kill -s TERM $MAINPID
+ExecReload=/bin/sh -c "/bin/kill -s HUP $(/bin/cat /var/run/nginx.pid)"
+ExecStop=/bin/sh -c "/bin/kill -s TERM $(/bin/cat /var/run/nginx.pid)"
 
 [Install]
 WantedBy=multi-user.target