Get the ManagedExecutor only once, better document the peculiarities … #1603

Job	Run time
build-and-run-jvm-tests	10m 23s
client native tests	10m 5s
hc5 native tests	8m 34s
logging native tests	8m 9s
metrics native tests	7m 42s
mtom native tests	6m 56s
mtom-awt native tests	7m 52s
server native tests	7m 3s
ws-addressing native tests	7m 3s
ws-rm native tests	11m 52s
ws-security-client native tests	9m 6s
ws-security-server native tests	9m 6s
ws-trust native tests	10m 2s
wsdl2java native tests	49s
wsdl2java-no-config native tests	41s
	1h 55m 23s

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