Change how scrollShift is calculated

In Firefox $('body').scrollTop returns 0, that's why the modal
appear outside the visible screen. Added $('hmtl).scrollTop.

var scrollShift = $('body').scrollTop() || $('html').scrollTop()

Closes-Bug: 1251361

Change-Id: Icf691eb140e091615a98f1fbd415428cd418ba9e
(cherry picked from commit 8950b90d1777e265f98379098cebef7517642efe)
fix help text in "Create An image" window

In the "Create An image" window, there are "minimum disk" and "minimun
memory" text input. But both help text on the two text inputs are using
"the minimum disk size...". Actually for the second one we should say
"the minimum memory size...", and now this patch fix this.

Change-Id: Ife19acba5fafb41d99e9416d2f9e8082b9eaef53
(cherry picked from commit 0314d54391775f09b35759a650dbae2e2ba567aa)
Merge "fix help text in "Create An image" window" into stable/havana
Merge "Change how scrollShift is calculated" into stable/havana