Apply busy indicator duration change of D22646 to the QQC2 style
Match the duration (2 seconds) that was set in D22630.
This style is mainly used by Plasma Mobile, therefore requesting team review from that project as well.
Reviewed By: VDG, ngraham
Subscribers: ngraham, kde-frameworks-devel
Differential Revision: https://phabricator.kde.org/D22720