After completing the installation of Leap 15.0 in /var/log/zypp/history I find this error:
# 2018-05-11 15:59:21 libzypp-plugin-appdata-1.0.1+git.20180327-lp150.1.1.noarch.rpm installed ok
# Additional rpm output:
# warning: %post(libzypp-plugin-appdata-1.0.1+git.20180327-lp150.1.1.noarch) scriptlet failed, exit status 6
# 

The scriptlet is the following:

if [ $1 == 1 ]; then
  ZYPP_PLUGIN_APPDATA_FORCE_COLLECT=1 zypper -n lr >/dev/null 2>&1
fi

because of the redirection it is not possible to get any error messages.
I have rebuild libzypp-plugin-appdata and taken out any redirection.
After completing a full OS installation using the modified rpm I get this error message in var/log/zypp/history:
# 2018-05-12 11:43:24 libzypp-plugin-appdata-1.0.1+git.20180327-lp150.1.1.1.noarch.rpm installed ok
# Additional rpm output:
# Warning: No repositories defined.
# Use the 'zypper addrepo' command to add one or more repositories.
# warning: %post(libzypp-plugin-appdata-1.0.1+git.20180327-lp150.1.1.1.noarch) scriptlet failed, exit status 6

to understand the reason of this scriptlet you have to look at bug 1009745.
However it is not clear to me if this is a real bug, or it is ok for the command to fail (the redirection would suggest so). If this is the case then changing the scriptlet like this:
if [ $1 == 1 ]; then
  ZYPP_PLUGIN_APPDATA_FORCE_COLLECT=1 zypper -n lr >/dev/null 2>&1
  :
fi
would get rid of the warning due to the exit status 6.