storage: Block acquire when PoSt reads are ongoing #49

Job	Run time
ci-lint	18s
build-2k	5m 0s
build-forest	4m 17s
build-calibnet	4m 37s
build-debug	5m 11s
build-mainnet	4m 35s
gen-check	5m 19s
lint	3m 7s
gofmt	19s
mod-tidy-check	41s
setup-params	4s
test (test-itest-curio, ./itests/curio_test.go)	4m 35s
test (test-all, `go list ./... \| grep -v curio/itests`)	2m 49s
test (test-itest-harmonyDB, ./itests/harmonydb_test.go)	2m 27s
test (test-itest-alertnow, ./itests/alertnow_test.go)	1m 36s
	44m 55s

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