SSH-channel should give the hostname instead of the hash when it warns that it can't connect to a runtime environment

(This issue is transferred from https://project.squashtest.org/browse/SQUASH-4268.)

When the SSH-channel fails to open a connection to a runtime environment, it displays the following WARNING:

WARNING in sshchannel: Could not reach host 0b8bda62-8ef8-47bc-86a5-fb22e0417a31:<XXX - detailed error message>

Instead of the hash, the host name of the execution environment (DNS or IP name) should be displayed so that the environment concerned can be more easily identified for the user.