webadmin: fix rendering issue in DetailsRenderer

Widgets like MemorySizeTextBoxLabel are inherited from ValueBoxBase.

ValueBoxBase uses input-text html element to display the data
as opposed to div/innerHtml used by ValueLabel.
So instead of taking the innerHtml from these fields,
DetailsRenderer will use getValue() to get the data.

Change-Id: I244819f17be801f8ba8c5c709e5127bd66567c81
Bug-Url: https://bugzilla.redhat.com/1049892
Signed-off-by: Kanagaraj M <kmayilsa@redhat.com>