Automated rpm package builds to '/usr'

This is instead of the default of '/usr/local'. Targeting '/usr'
is more in line with what most RPM distros expect.

script/rpmbuild

@@ -3,4 +3,4 @@
 set -e
 
 script/build
-script/grunt mkrpm publish-build --stack
+script/grunt mkrpm publish-build --stack --install-dir /usr