Description of problem:

When running https://github.com/adelton/docker-freeipa with RHEL 7.3 nightly,
the ipa-server-install fails because in unprivileged container, hostnamectl
set-hostname fails.

Version-Release number of selected component (if applicable):

ipa-server-4.4.0-1.el7.x86_64

How reproducible:

Deterministic.

Steps to Reproduce:
1. Build container image based on RHEL 7.3 nightly repo / upgraded to this
content.
2. Run the container: docker run -t --name freeipa-server-container -h
ipa.example.test -v /dev/urandom:/dev/random:ro -v
/opt/ipa-data-rhel-7.3-nightly:/data -v /sys/fs/cgroup:/sys/fs/cgroup:ro
--cap-add=SYS_TIME  freeipa-server

Actual results:

systemd 219 running in system mode. (+PAM +AUDIT +SELINUX +IMA -APPARMOR +SMACK
+SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ -LZ4 -SECCOMP +BLKID
+ELFUTILS +KMOD +IDN)
Detected virtualization docker.
Detected architecture x86-64.
Set hostname to <ipa.example.test>.
Thu Jul  7 16:14:35 EDT 2016 /usr/sbin/ipa-server-configure-first
systemd-tmpfiles-setup.service: main process exited, code=exited,
status=1/FAILURE
Job container-ipa.target/start failed with result 'dependency'.
Unit systemd-tmpfiles-setup.service entered failed state.
systemd-tmpfiles-setup.service failed.
ipa         : ERROR    Failed to set this machine hostname to ipa.example.test
(Command '/bin/hostnamectl set-hostname ipa.example.test' returned non-zero
exit status 1).
ipa.ipapython.install.cli.install_tool(Server): ERROR    Command
'/bin/hostnamectl set-hostname ipa.example.test' returned non-zero exit status
1
ipa.ipapython.install.cli.install_tool(Server): ERROR    The ipa-server-install
command failed. See /var/log/ipaserver-install.log for more information
Checking DNS domain example.test, please wait ...

The log file for this installation can be found in
/var/log/ipaserver-install.log
==============================================================================
This program will set up the IPA Server.

This includes:
  * Configure a stand-alone CA (dogtag) for certificate management
  * Configure the Network Time Daemon (ntpd)
  * Create and configure an instance of Directory Server
  * Create and configure a Kerberos Key Distribution Center (KDC)
  * Configure Apache (httpd)
  * Configure DNS (bind)

Warning: skipping DNS resolution of host ipa.example.test
Checking DNS domain example.test., please wait ...
Checking DNS forwarders, please wait ...

The IPA Master Server will be configured with:
Hostname:       ipa.example.test
IP address(es): 172.17.0.2
Domain name:    example.test
Realm name:     EXAMPLE.TEST

BIND DNS server will be configured to serve IPA domain with:
Forwarders:       10.16.36.29
Forward policy:   only
Reverse zone(s):  No reverse zone

FreeIPA server configuration failed.

Expected results:

No error.

Additional info:

The problem seems to come from change c5686295f14c955d34d9598ddb80b30cb9df663c.

Note that in containers, we rely on the hostname being set from "outside", in
docker run case with -h option. The installer should not run hostnamectl when
the hostname is already set to the required value.