dashboard: add /opt/freeware/bin to PATH on aix builder
dashboard: add /opt/freeware/bin to PATH on aix builder

Updates golang/go#29065
Fixes golang/go#29078

Change-Id: Ifa9355c9dc988a460b6198913431647ec2c5e6ac
Reviewed-on: https://go-review.googlesource.com/c/152457
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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