jobs: yml files: set vim expandtab (and shiftwidth)

Having tabs in the yml files cause parse errors. For vim convenience, add
comments that instruct vim to expand the tabs to spaces.

Change-Id: I5f0598a31e30d1a9440c40935644bb782f645664

jobs/gerrit-verifications.yml

@@ -265,3 +265,5 @@
            console-log-parsers:
              - 'GNU C Compiler 4 (gcc)'
            resolve-relative-paths: true
+
+# vim: expandtab tabstop=2 shiftwidth=2

jobs/osmocom-nightly-nitb-split.yml

@@ -20,3 +20,5 @@
           git-config-email: 'jenkins@osmocom.org'
     triggers:
       - timed: "@midnight"
+
+# vim: expandtab tabstop=2 shiftwidth=2

jobs/osmocom-obs-latest.yml

@@ -20,3 +20,5 @@
           git-config-email: 'jenkins@osmocom.org'
     triggers:
       - timed: "@midnight"
+
+# vim: expandtab tabstop=2 shiftwidth=2