tpm2_createpolicy: flush session for trial policy. #1847

Job	Run time
master-tss-build-test (gcc)	17m 57s
coverage-test	6m 15s
master-tss-build-test (clang)	4m 51s
build-test (ubuntu-20.04, gcc)	5m 53s
coverity-test	0s
build-test (ubuntu-20.04, clang)	5m 1s
build-test (fedora-30, gcc)	5m 58s
build-test (fedora-30, clang)	5m 29s
build-test (opensuse-leap, gcc)	6m 1s
build-test (opensuse-leap, clang)	5m 16s
build-test (fedora-32, gcc)	5m 51s
build-test (fedora-32, clang)	5m 10s
build-test (ubuntu-22.04, gcc)	11m 13s
build-test (ubuntu-22.04, clang)	10m 46s
	1h 35m 41s

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