Keep retrying in waitFindObjectOrNull() until timeout is reached

Partner discovered that waitFindObject() actually doesn't wait for the
full timeout so that it is failing to find UI objects on slower devices
even if they use a longer timeout.

Bug: 388955671
Flag: EXEMPT TEST_ONLY
Test: presubmit
Change-Id: I8ba57e8ed5222c84aed2bed2e08dd8e2688d13a9