XE-1404: Switch to Flamingo Skin by default.

* Fix some integration tests.
XWIKI-10699: Make sure the Search button is the same size as the input
XE-1404: Switch to Flamingo Skin by default.

* Fix some integration tests.
[tests] Failing the build if the started test XWiki instance fails to stop.
XWIKI-10737: Make Administration responsive