Change ubi so it only creates the install directory once it's downloa… #443

Job	Run time
Alpine Linux	1m 31s
FreeBSD-x86_64 with rust stable	1m 4s
Linux-x86_64 with rust stable	1m 29s
Linux-x86_64 (rustls-native-roots) with rust stable	1m 25s
Linux-x86_64 (native-tls) with rust stable	1m 30s
Linux-x86_64 (native-tls-vendored) with rust stable	1m 43s
Linux-aarch64 with rust stable	1m 25s
Linux-arm with rust stable	1m 18s
Linux-i686 with rust stable	52s
Linux-powerpc with rust stable	53s
Linux-powerpc64 with rust stable	51s
Linux-powerpc64le with rust stable	47s
Linux-riscv64 with rust stable	1m 4s
Linux-s390x with rust stable	57s
NetBSD-x86_64 with rust stable	1m 43s
Windows-aarch64 with rust stable	28s
Windows-i686 with rust stable	30s
Windows-x86_64 with rust stable	28s
macOS-x86_64 with rust stable	1m 30s
macOS-aarch64 with rust stable	1m 29s
Linux-x86_64 with rust beta	1m 28s
Linux-x86_64 with rust nightly	1m 18s
	25m 43s

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