Progress bar text initializes and resets

[binhonglee]

Existing behavior for installation progress bar text :

• Before installation : no changes (empty when initialized, stays at 100% when continued from previous installation instead of reset to empty or to 0%)

Behavior after this change :

• Before installation : initializes (or reset) to 0% along with all other relevant components (progressbar.set_fraction and progresslabel)

[JosephMcc]

It would be nice to see a description of what you are fixing as part of the actual commit message. It makes things more clear when you are looking at the history down the road.

Example: be31728