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: I1d03ac87a7d0c3c600d187f3e485cb2dab8838bb
diff --git a/.gitignore b/.gitignore
index 900c09c..d3324bb 100644
--- a/.gitignore
+++ b/.gitignore
@@ -61,3 +61,5 @@
 doc/manuals/osmomsc-usermanual.xml
 doc/manuals/common
 doc/manuals/build
+
+contrib/osmo-mgw.spec