Fix some bugs in xds flow control #2319

Job	Run time
build agent and cache	1m 57s
download midwares and cache	13s
set-execution-conditions	11s
Test for spring (1.5.0.RELEASE, Edgware.SR2, 1.5.0.RELEASE)	15m 52s
Test for spring (2.0.2.RELEASE, Finchley.RELEASE, 4.1.3, 2.0.0.RELEASE, 1.0.1)	15m 40s
Test for spring (2.1.0.RELEASE, Greenwich.RELEASE, 4.2.6, 2.1.0.RELEASE, 1.0.1)	15m 22s
Test for spring (2.2.0.RELEASE, Hoxton.RELEASE, 4.3.6, 2.2.0.RELEASE, 1.0.3)	15m 27s
Test for spring (2.3.0.RELEASE, Hoxton.RELEASE, 4.4.1, 2.2.8.RELEASE, 1.1.2)	15m 3s
Test for spring (2.4.0, 2020.0.0, 4.5.6, 2021.0.1.0, 1.1.4)	14m 44s
Test for spring (2.6.2, 2021.0.0, 4.5.10, 2021.1, 1.1.10)	14m 54s
Test for spring (2.7.2, 2021.0.3, 4.5.13, 1.1.12)	14m 0s
	2h 3m 23s

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