Fix #3973 - Unneeded datastore option URI

This fixes #3973.

When Glassfish is installed, the web root is always /, so there is no point to make this arbitrary.

## To set up Glassfish:

- [ ] Windows is the easiest to set up, so get a Windows VM up and ready. Windows 2003 SP2 or Win 7 should be fine.
- [ ] Download and install JDK8: http://www.oracle.com/technetwork/java/javase/downloads/jdk8-downloads-2133151.html
- [ ] Download Glassfish 4: http://download.java.net/glassfish/4.0/release/glassfish-4.0.zip
- [ ] Extract glassfish-4.0.zip
- [ ] In command prompt, go to directory glassfish4\bin\
- [ ] Run ```asadmin```, which is the admin console.
- [ ] Enter ```start-domain domain1```
- [ ] Open a browser, and then go to: http://localhost:4848
- [ ] Look at the menu on the left, there should be an item that says "Domain". Click on that.
- [ ] On the right, there should be an "Administrator Password" tab. Click on that, and go change your admin password. You need to do this for Secure Administration.
- [ ] Again, look at the menu on the left, click on "server(Admin Server)"
- [ ] You should see a button that says "Enable Secure Admin", click on that.
- [ ] After you enable Secure Admin, Glassfish will have to restart. Wait for a few seconds, and then go to command prompt, make sure port 4848 is up again. You can also try to login remotely to double check if you want.

## To test the module

- [ ] Start ```msfconsole```
- [ ] ```use auxiliary/scanner/http/glassfish_login```
- [ ] ```set password [PASSWORD]```
- [ ] ```set rhosts [IP]```
- [ ] ```run```
- [ ] Make sure the module can login

An example for the above test should look like this:

```
msf auxiliary(glassfish_login) > run

[*] 192.168.1.106:4848 GLASSFISH - Checking if Glassfish requires a password...
[*] 192.168.1.106:4848 GLASSFISH - Glassfish is protected with a password
[+] 192.168.1.106:4848 GLASSFISH - Success: 'admin:asdf'
[*] Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed
msf auxiliary(glassfish_login) >
```
I guess I'm missing something, but isn't ```uri``` required :? 

https://github.com/rapid7/metasploit-framework/blob/master/lib/metasploit/framework/login_scanner/http.rb#L26