cmd/oracle: expect oracle binary beneath $GOBIN, $GOPATH/bin, or $GOROOT/bin
cmd/oracle: expect oracle binary beneath $GOBIN, $GOPATH/bin, or $GOROOT/bin

in that order, so that "go get golang.org/x/tools/cmd/oracle" installs
it and no copy is needed.  We keep the old location for compatibility.

Why is if/else control flow so hard in basic Lisp?  Sometimes you just need 'return'.

Change-Id: Iae231a761d707daaa1316161cfad0365111eff0e
Reviewed-on: https://go-review.googlesource.com/9547
Reviewed-by: David Chase <ae171625adc8645b8b79b7e405a6da5aba5341e0@google.com>

golang/tools,cmars/tools,josharian/tools,runcom/tools,sshetty10/tools,syreclabs/go-tools,springning/tools,magiccao/tools,golang/tools,josharian/tools,cmars/tools,argandas/tools,josharian/tools,glasser/golang-tools,syreclabs/go-tools,cw2018/tools,cmars/tools,matryer/tools,glasser/golang-tools,syreclabs/go-tools,magiccao/tools,syreclabs/go-tools,argandas/tools,matryer/tools,runcom/tools,sshetty10/tools,runcom/tools,golang/tools,josharian/tools,jdhenke/tools,nicot/tools,springning/tools,glasser/golang-tools,magiccao/tools,syreclabs/go-tools,golang/tools,syreclabs/go-tools,nicot/tools,jdhenke/tools,nicot/tools,argandas/tools,springning/tools,jdhenke/tools,sshetty10/tools,glasser/golang-tools,argandas/tools,sshetty10/tools,jdhenke/tools,nicot/tools,springning/tools,magiccao/tools,cmars/tools,golang/tools,cw2018/tools,matryer/tools,cw2018/tools,cw2018/tools,runcom/tools,matryer/tools