Workaround Streaming Push unreliabilities (#13415)

Change-Id: I5e946b365e22e71a0c13606fcd159d1ce7c82925
Merge commit '06d0cf4daa414eca3c2a73df8171706ca7012213'

Conflicts:
	uitest/src/com/vaadin/tests/push/PushConfigurationTest.java

Change-Id: Ifb458fce1a9a1fa84d935b893f5af1931951058c