cmd/dlv: print error when build fails in 'dlv test' (#2127)
cmd/dlv: print error when build fails in 'dlv test' (#2127)

Fixes #2126
aarzilli/delve,aarzilli/delve,go-delve/delve,go-delve/delve,go-delve/delve,go-delve/delve,go-delve/delve,aarzilli/delve,aarzilli/delve