Auxiliary module to HP LaserJet Printer SNMP Enumeration (redux)

This module allows enumeration of files previously printed via SNMP request. It provides details as filename, client, timestamp and username informations. The default community used is "public".
(old request: http://dev.metasploit.com/redmine/issues/6864).

```
msf auxiliary(snmp_enum_hp_laserjet) > set RHOSTS 1.2.3.4
RHOSTS => 1.2.3.4
msf auxiliary(snmp_enum_hp_laserjet) > run

[+] IP address  : 1.2.3.4
[+] Hostname    : HPPRINTERTEST
[+] Description : HP ETHERNET MULTI-ENVIRONMENT,ROM none,JETDIRECT,JD102,EEPROM V.34.63,CIDATE 02/26/2007
[+]
[+] File name   : Secret.pdf
[+] Username    : Jack
[+] Client      : HOSTNAME1
[+] Timestamp   : 20140106170130
[+]
[+] File name   : Test.doc
[+] Username    : Mark
[+] Client      : HOSTNAME2
[+] Timestamp   : 20140106170246
...
..
.
```

(Copied from #2919.)

```
wvu@kharak:~/metasploit-framework:feature/laserjet$ git cherry-pick -x HEAD~..upstream/pr/2919
[feature/laserjet ae53d75] Module to HP LaserJet Printer SNMP Enumeration
 Author: Matteo Cantoni <matteo.cantoni@gmail.com>
 1 file changed, 148 insertions(+)
 create mode 100644 modules/auxiliary/scanner/snmp/snmp_enum_hp_laserjet.rb
[feature/laserjet c559a6b] fix description
 Author: Matteo Cantoni <matteo.cantoni@gmail.com>
 1 file changed, 4 insertions(+), 2 deletions(-)
wvu@kharak:~/metasploit-framework:feature/laserjet$ 
```

See https://github.com/rapid7/metasploit-framework/pull/2996#issuecomment-38973604 for why we have to do this.