Fix Alpine and Mariner /etc/hosts templates

[dermotbradley]

Proposed Commit Message

Fix Alpine and Mariner /etc/hosts templates

Revert the changes I introduced with #1084, these had the side-effect
of causing "hostname" problems. Fixes #4771.

Also remove the "::1 {{fqdn}} {{hostname}}" entry as this being present
results in strange behaviour with "hostname -i" command: Busybox
returns "127.0.0.1", or "127.0.0.1 A.B.C.D" if an additional
non-loopback IP entry in /etc/hosts), Coreutils and net-tools both
return "::1" in both situations, whereas if the "::1" entry is removed
then Busybox, Coreutils, and net-tools "hostname -i" all behave in the
same fashion returning "127.0.0.1" or "127.0.0.1 A.B.C.D" as appropriate.

Also correct hosts.mariner.tmpli file it was not valid (every line
was prefixed with "+").

Fixes GH-4771

Additional Context

Test Steps

Checklist

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

Merge type

• Squash merge using "Proposed Commit Message"
• Rebase and merge unique commits. Requires commit messages per-commit each referencing the pull request number (#<PR_NUM>)

[holmanb]

LGTM