improve instructions for timezone screen

[Yousuf 'Jay' Philips]

In various testcases, the instructions for the 'Where are you?' screen can be improved.

- before -

X. If your system is connected to the network, note the preselected timezone correspond with your timezone and the city indicated in the text box
    The timezone and city displayed match your timezone and the main city from your area
X. Select your timezone, and click on the continue button

- after -

X. If your system is connected to the internet, note the preselected timezone and the city indicated in the text box
    The timezone and city displayed match your timezone and the main city from your area
X. Select your timezone if necessary, and click on the Continue button

http://iso.qa.ubuntu.com/qatracker/testcases/1301/info
http://iso.qa.ubuntu.com/qatracker/testcases/1300/info