MTL-2088 Fix build race condition (#57)

Variables need a `def` in order to be unique/re-defined
within each `matrix` build, otherwise there is a risk of
a race condition happening. The race condition occurs
when one `matrix` build redefines (reuses) the variables
while the variables are being read by another `matrix` build.

In MTL-2088, an SP4 build was publishing RPMs when the SP3
`matrix` build updated these variables, leading to some of
the SP4 RPMs to end up in the SP3 drop-off.

Jenkinsfile.github

@@ -98,9 +98,9 @@ pipeline {
                     stage('Publish: RPMs') {
                         steps {
                             script {
-                                sles_version_parts = "${sleVersion}".tokenize('.')
-                                sles_major = "${sles_version_parts[0]}"
-                                sles_minor = "${sles_version_parts[1]}"
+                                def sles_version_parts = "${sleVersion}".tokenize('.')
+                                def sles_major = "${sles_version_parts[0]}"
+                                def sles_minor = "${sles_version_parts[1]}"
                                 publishCsmRpms(
                                         arch: "noarch",
                                         component: env.NAME,