Fix subunit2sql install guard for idempotency
The exec to install subunit2sql tries to compare the output of pip list
versus pip search to determine whether it is on the latest version.
Without this patch, the pip list command produces a string that has too
many spaces on the end and therefore doesn't match the result of the pip
search command. This means that it will always try to reinstall
subunit2sql even when it doesn't need to, which breaks idempotency
tests. This patch fixes the regex group to exclude trailing spaces.