grml-hostname does not modify /etc/hosts correctly as the regex for modifying /etc/hosts is wrong.

Besides fixing the regex we should ship libnss-myhostname to prevent any problems due to manually 
adjusting the hostname.


Example:

(1)-~/src/grml-scripts$ cat /etc/hosts                                                            
127.0.0.1	localhost pisa-vm
::1		localhost ip6-localhost ip6-loopback
fe00::0		ip6-localnet
ff00::0		ip6-mcastprefix
ff02::1		ip6-allnodes
ff02::2		ip6-allrouters


2)-~/src/grml-scripts$ sudo grml-hostname foobar                                                 
Setting hostname to foobar: done
(3)-~/src/grml-scripts$ cat /etc/hosts                                                            
127.0.0.1	localhost pisa-vm
::1		localhost ip6-localhost ip6-loopback
fe00::0		ip6-localnet
ff00::0		ip6-mcastprefix
ff02::1		ip6-allnodes
ff02::2		ip6-allrouters