CP-9795: Improve comparison of hostname against localhost

On RHEL-based systems prior to 7, the output of hostname with no
hostname setup is "localhost.localdomain".  On RHEL 7-based systems and
Debian-based systems, the output of hostname is "localhost".  Compare
the name label against either of these values for resilience.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
To avoid repeating `Db.Host.get_name_label ~__context ~self:localhost` we could have something like
```
let label = Db.Host.get_name_label ~__context ~self:localhost in
if label = "localhost.localdomain" || label = "localhost" then
```
or 
```
if List.mem (Db.Host.get_name_label ~__context ~self:localhost) ["localhost"; "localhost.localdomain"] then
```
or even
```
match Db.Host.get_name_label ~__context ~self:localhost with
	| "localhost"
	| "localhost.localdomain" ->
...etc.
```
(but that last one is more cumbersome given the need to include a do-nothing match action for `_`.)