Multiple concurrent invocations of ydbinstall / ydbinstall.sh work correctly

Final Release Note

Multiple concurrent invocations of ydbinstall / ydbinstall.sh work correctly. Previously, owing to a race condition, this could result in unpredictable results. This edge condition was only detected in in-house development and test environments, and was never reported by a user. [#855 (closed)]

Description

Low priority issue, as it's not a thing users will actually do; and we are planning to sunset the use of the ./configure.gtc script anyways (#618).

See discussion here: !1144 (comment 857811803) and further down here: !1144 (comment 858819367).

Draft Release Note