One of the 'go build' commands executed by this test passed the '-i'
flag, which caused the 'go' command to attempt to install transitive
standard-library dependencies to GOROOT/pkg/$GOOS_$GOARCH_dynlink.
That failed if GOROOT/pkg was not writable (for example, if GOROOT was
owned by the root user, but the user running the test was not root).
As far as I can tell the '-i' flag is not necessary in this test.
Prior to the introduction of the build cache it may have been an
optimization, but now that the build cache is required the '-i' flag
only adds extra work.