travis: fix build process
Created by: kortschak
We have been seeing no-output time outs for OpenBLAS recently. This is an attempt to mitigate that.
During looking at the process I noticed that we don't seem to output the OpenBLAS sha1 anymore, the second commit restores that behaviour.
Finally, it appears that travis-ci have changed how they are shelling things and setting CGO_LDFLAGS only once at the site of install does not impact on the env of the go test invocation, so it is added there in the third commit.
Please take a look.