Feature: Added option to also show domain if the hostname is shown

Added possibility to show domain if host name is shown.

I've added the option LP_DOMAIN to show the domain if the host name is shown.
I also edited the test.sh file to test for new feature.

I'm using the command ```hostname -f``` instead of the ```\H``` (for bash) and ```%M```(for zsh)
because I noticed that the ```\H``` is bash is not the same in all systems (zsh is coherent):

In macos (bash 3.2.48(1)-release) and freeBSD(bash 4.2.45(0)-release) :
```
# hostname -f
host.domain
# export PS1=" \\\h=\h \\\H=\H #"
 \h=host \H=host.domain #
```
In linux: SLC6 (bash: 4.1.2(1)-release), debian(bash:4.2.37(1)-release ) and ubunto(bash: 4.2.25(1)-release) ):

```
# hostname -f
host.domain
# export PS1=" \\\h=\h \\\H=\H #"
 \h=host \H=host #
```