dashboard: test sub-repositories on s390x
dashboard: test sub-repositories on s390x

Fixes golang/go#26131

Change-Id: I07e84c255a158b843168612cc3dad7688343ffb7
Reviewed-on: https://go-review.googlesource.com/127375
Reviewed-by: Michael Munday <19411bdeea90f848b8e02e9a1c63a7ce7cc699ea@ibm.com>
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>

golang/build,golang/build,golang/build,golang/build