Description of problem:

In disk druid , during GUI install, when adding ( creating ) a new partition, 
the input for the size does not work correctly. When a value is entered manualy 
and then the cursor-up/down key is used, the value does not increase/decrease 
from the entered value, but from the previous value.

Version-Release number of selected component (if applicable):

redhat linux/x86 8.0.92 (phoebe)

How reproducible:


Steps to Reproduce:
1. In DD click "Add Partition"
2. Enter a new size, like 500 ( originally 100 is written in the text field )
3. Press CURSOR_UP
    
Actual results:

the value changes to 101

Expected results:

the value changes to 501

Additional info:

If you press CURSOR_DOWN, then it goes 99,98,97... instead of 499,498,497 ...