misc/android: enable many more tests on GOOS=android
Android tests are built on the host and run on the device. To do
that, the exec wrapper copies the test binary and testdata to the device.
To enable many more tests, make the copied environment more like the host:
- Copy all of pkg from GOROOT, not just the android pkg directory.
- Copy any parent testdata directories as well as the package's own.
- Copy *.go files from the package directory. This enables misc/cgo/stdio
and misc/cgo/life tests that were invisible before so disable them explicitly.
- Always copy the GOROOT, even for tests outside GOROOT. This is expensive
but only done once per make.bash.
- Build the go tool for the device and put it in PATH. Set GOCACHE
to a writable directory and disable cgo.
While here, use a single directory for all the exec wrapper files and
delete that once per make.bash as well.
In total, this CL enables many tests in the subrepos that would need skips
without it, in particular the x/tools tests.