[6.15.z] Fix test_positive_mismatched_satellite_fqdn

[Satellite-QE]

Cherrypick of PR: #16796

Test seemed to randomly fail on assertion at

robottelo/tests/foreman/destructive/test_installer.py

Line 109 in 952b960

assert facter_command_output != hostname_command_output

After some investigation I found out that the domain is being generated randomly and for some domains (e.g. test.com, test.biz) the output of hostname --fqdn returns FQDN, not just "shortname" as we expected.

Removing nameservers from /etc/resolv.conf solves the issue.

> hostnamectl set-hostname testname # set test hostname
> echo "search example.info" > /etc/resolv.conf # set search domain to example.info
> hostname --fqdn # hostname prints only hostname without domain name
testname
> sed -i "s/^search.*/search test.biz/" /etc/resolv.conf # set search domain to test.biz
> hostname --fqdn # for some reason the fqdn is printed
testname.test.biz
> sed -i "/nameserver.*/d" /etc/resolv.conf # remove nameservers
> hostname --fqdn # only hostname without domain name is printed
testname

[Satellite-QE]

trigger: test-robottelo
pytest: tests/foreman/destructive/test_installer.py -k test_positive_mismatched_satellite_fqdn

[Satellite-QE]

PRT Result

Build Number: 9235
Build Status: SUCCESS
PRT Comment: pytest tests/foreman/destructive/test_installer.py -k test_positive_mismatched_satellite_fqdn --external-logging
Test Result : ========== 1 passed, 4 deselected, 17 warnings in 1107.53s (0:18:27) ===========