contrib: integrate RPM spec

Remove OpenSUSE bug report link, set version to @VERSION@, make it build
with CentOS 8 etc.

Related: OS#4550
Change-Id: If5499e11d872e629a018fc77d5adf5d0cb863d48
diff --git a/configure.ac b/configure.ac
index 984c627..1e0740e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -267,4 +267,5 @@
     doc/sequence_charts/Makefile
     contrib/Makefile
     contrib/systemd/Makefile
+    contrib/osmo-msc.spec
     Makefile)