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: I824b67f2d590ac2aa9f2e4fa4387a5283cf22521
diff --git a/.gitignore b/.gitignore
index b3e50f5..546d5df 100644
--- a/.gitignore
+++ b/.gitignore
@@ -69,3 +69,5 @@
 doc/manuals/osmomsc-usermanual.xml
 doc/manuals/common
 doc/manuals/build
+
+contrib/osmo-sgsn.spec