Bug 1369092

Description of problem:
In case of trying to re-install host, If host changed his SSH fingerprint,
the following error will be in the events tab: 

Host <host name> installation failed. Invalid fingerprint SHA256:+rQeBegZiDek/+b50NXoW/IDVRcwpWYOEYx4YpnLtEg, expected SHA256:PhhVQGc1wyYljj4EAVLCtf/fKSDE5foFZrMnQEPyjlY.

I this case, the behaviour should be the same as connecting this host in ssh.
It means that the user will get a notification about the change of fingerprint,
and will decided if he wants to fetch the fingerprint from the host. 

The reason is that the fetch option is under Edit host -> General -> advanced parameters. and it's not so user friendly.

The ssh message:
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@       WARNING: POSSIBLE DNS SPOOFING DETECTED!          @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
The RSA host key for lilach-vdsb.tlv.redhat.com has changed,
and the key for the corresponding IP address 10.35.5.48
has a different value. This could either mean that
DNS SPOOFING is happening or the IP address for the host
and its host key have changed at the same time.
Offending key for IP in /home/mshira/.ssh/known_hosts:8
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
SHA256:+rQeBegZiDek/+b50NXoW/IDVRcwpWYOEYx4YpnLtEg.
Please contact your system administrator.
Add correct host key in /home/mshira/.ssh/known_hosts to get rid of this message.
Offending RSA key in /home/mshira/.ssh/known_hosts:144
RSA host key for lilach-vdsb.tlv.redhat.com has changed and you have requested strict checking.
Host key verification failed.