If during the installation I select to install the package ctags, I
found this error in /var/log/zypp/history:

# 2016-04-20 20:34:48 ctags-5.8-8.2.x86_64.rpm installed ok
# Additional rpm output:
# /var/tmp/rpm-tmp.qve5Uo: line 1: rm: command not found
# update-alternatives: using /usr/bin/ctags-exuberant to provide /usr/bin/ctags
(ctags) in auto mode
# 
2016-04-20
20:34:48|install|ctags|5.8-8.2|x86_64||openSUSE-42.1-0|3bb1753b7172867ca87203e96201544dfa7a2081|

The problem is that ctags is installed before coreutils and at that time the
binariy rm, used in the postinstall scriptlet, is not available yet.

A possible fix is to add this line in ctags.spec:

 BuildRequires:  update-alternatives
 PreReq:         update-alternatives
+PreReq:         coreutils