network-ups-tools: fix upsdrvctl service

upsdrvctl will not stay in the foreground, even with -D. It will start
drivers and quit. Use pause, and a separate finish script to kill the
drivers.

srcpkgs/network-ups-tools/files/upsdrvctl/finish

@@ -0,0 +1,2 @@
+#!/bin/sh
+upsdrvctl -D stop

srcpkgs/network-ups-tools/files/upsdrvctl/run

@@ -1,4 +1,5 @@
 #!/bin/sh
 # Network UPS Tools - driver controller
 install -d -m 0770 -o nut -g nut /run/ups
-exec upsdrvctl -D start
+upsdrvctl -D start
+exec chpst -b upsdrvctl pause