os: /system/framework doesn't exist on brillo; tests fail for GOOS=android on brillo

[rakyll]

Reproducible on Qualcomm Dragonboard 410c, Brillo image built with BDK 7.5.4.

go_android_exec: adb shell mkdir -p /mnt/media_rw/tmp/os.test-55422
go_android_exec: adb push /var/folders/00/1b8h8000h01000cxqpysvccm005d21/T/go-build559449628/os/_test/os.test /mnt/media_rw/tmp/os.test-55422/os.test-55422-tmp
1208 KB/s (3147688 bytes in 2.544s)
go_android_exec: adb shell cp '/mnt/media_rw/tmp/os.test-55422/os.test-55422-tmp' '/mnt/media_rw/tmp/os.test-55422/os.test-55422'
go_android_exec: adb shell rm '/mnt/media_rw/tmp/os.test-55422/os.test-55422-tmp'
go_android_exec: adb shell export TMPDIR="/mnt/media_rw/tmp/os.test-55422"; export GOROOT="/mnt/media_rw/goroot/"; export GOPATH="/mnt/media_rw/gopath/"; cd "/mnt/media_rw/goroot/src/os"; '/mnt/media_rw/tmp/os.test-55422/os.test-55422' -test.short=true -test.timeout=6m0s; echo -n exitcode=$?
--- FAIL: TestStat (0.00s)
    os_test.go:167: stat failed: stat /system/framework/ext.jar: no such file or directory
--- FAIL: TestFstat (0.00s)
    os_test.go:182: open failed: open /system/framework/ext.jar: no such file or directory
--- FAIL: TestLstat (0.00s)
    os_test.go:202: lstat failed: lstat /system/framework/ext.jar: no such file or directory
--- FAIL: TestRead0 (0.00s)
    os_test.go:218: open failed: open /system/framework/ext.jar: no such file or directory
--- FAIL: TestReaddirnames (0.00s)
    os_test.go:237: open "/system/framework" failed: open /system/framework: no such file or directory
--- FAIL: TestReaddir (0.00s)
    os_test.go:266: open "/system/framework" failed: open /system/framework: no such file or directory
--- FAIL: TestOpenError (0.00s)
    os_test.go:1265: Open("/system/framework", 1) = _, "no such file or directory"; want "is a directory"
    os_test.go:1265: Open("/system/framework/ext.jar/no-such-file", 1) = _, "no such file or directory"; want "not a directory"
FAIL
exitcode=1go_android_exec: adb shell rm -rf /mnt/media_rw/tmp/os.test-55422

[gopherbot]

CL https://golang.org/cl/19904 mentions this issue.