systemd: Use non-absolute paths in Exec* lines

Since systemd v239, Exec* binaries are resolved from PATH when they
are not-absolute. Switch to this by default for ease of downstream
maintenance. Many downstream distributions move individual binaries
to locations that existing compile-time configurations cannot
accommodate.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Dimitri John Ledkov <dimitri.ledkov@canonical.com>
Closes #14880

etc/systemd/system/zfs-import-cache.service.in

@@ -15,7 +15,7 @@ ConditionPathIsDirectory=/sys/module/zfs
 Type=oneshot
 RemainAfterExit=yes
 EnvironmentFile=-@initconfdir@/zfs
-ExecStart=@sbindir@/zpool import -c @sysconfdir@/zfs/zpool.cache -aN $ZPOOL_IMPORT_OPTS
+ExecStart=zpool import -c @sysconfdir@/zfs/zpool.cache -aN $ZPOOL_IMPORT_OPTS
 
 [Install]
 WantedBy=zfs-import.target

etc/systemd/system/zfs-import-scan.service.in

@@ -14,7 +14,7 @@ ConditionPathIsDirectory=/sys/module/zfs
 Type=oneshot
 RemainAfterExit=yes
 EnvironmentFile=-@initconfdir@/zfs
-ExecStart=@sbindir@/zpool import -aN -o cachefile=none $ZPOOL_IMPORT_OPTS
+ExecStart=zpool import -aN -o cachefile=none $ZPOOL_IMPORT_OPTS
 
 [Install]
 WantedBy=zfs-import.target

etc/systemd/system/zfs-mount.service.in

@@ -12,7 +12,7 @@ ConditionPathIsDirectory=/sys/module/zfs
 Type=oneshot
 RemainAfterExit=yes
 EnvironmentFile=-@initconfdir@/zfs
-ExecStart=@sbindir@/zfs mount -a
+ExecStart=zfs mount -a
 
 [Install]
 WantedBy=zfs.target

etc/systemd/system/zfs-scrub@.service.in

@@ -8,8 +8,8 @@ ConditionPathIsDirectory=/sys/module/zfs
 
 [Service]
 EnvironmentFile=-@initconfdir@/zfs
-ExecStart=/bin/sh -c '\
+ExecStart=sh -c '\
-if @sbindir@/zpool status %i | grep -q "scrub in progress"; then\
+if zpool status %i | grep -q "scrub in progress"; then\
-exec @sbindir@/zpool wait -t scrub %i;\
+exec zpool wait -t scrub %i;\
-else exec @sbindir@/zpool scrub -w %i; fi'
+else exec zpool scrub -w %i; fi'
-ExecStop=-/bin/sh -c '@sbindir@/zpool scrub -p %i 2>/dev/null || true'
+ExecStop=-sh -c 'zpool scrub -p %i 2>/dev/null || true'

etc/systemd/system/zfs-share.service.in

@@ -14,7 +14,7 @@ ConditionPathIsDirectory=/sys/module/zfs
 Type=oneshot
 RemainAfterExit=yes
 EnvironmentFile=-@initconfdir@/zfs
-ExecStart=@sbindir@/zfs share -a
+ExecStart=zfs share -a
 
 [Install]
 WantedBy=zfs.target

etc/systemd/system/zfs-trim@.service.in

@@ -8,8 +8,8 @@ ConditionPathIsDirectory=/sys/module/zfs
 
 [Service]
 EnvironmentFile=-@initconfdir@/zfs
-ExecStart=/bin/sh -c '\
+ExecStart=sh -c '\
-if @sbindir@/zpool status %i | grep -q "(trimming)"; then\
+if zpool status %i | grep -q "(trimming)"; then\
-exec @sbindir@/zpool wait -t trim %i;\
+exec zpool wait -t trim %i;\
-else exec @sbindir@/zpool trim -w %i; fi'
+else exec zpool trim -w %i; fi'
-ExecStop=-/bin/sh -c '@sbindir@/zpool trim -s %i 2>/dev/null || true'
+ExecStop=-sh -c 'zpool trim -s %i 2>/dev/null || true'

etc/systemd/system/zfs-volume-wait.service.in

@@ -9,7 +9,7 @@ ConditionPathIsDirectory=/sys/module/zfs
 Type=oneshot
 RemainAfterExit=yes
 EnvironmentFile=-@initconfdir@/zfs
-ExecStart=@bindir@/zvol_wait
+ExecStart=zvol_wait
 
 [Install]
 WantedBy=zfs-volumes.target

etc/systemd/system/zfs-zed.service.in

@@ -5,7 +5,7 @@ ConditionPathIsDirectory=/sys/module/zfs
 
 [Service]
 EnvironmentFile=-@initconfdir@/zfs
-ExecStart=@sbindir@/zed -F
+ExecStart=zed -F
 Restart=always
 
 [Install]