Kris

Add a retry for stapling

1

Similar to the wait for notarize, occasionally staple will fail with a timeout to cloudkit servers, forcing a new build.

### Issue Description ``` goroutine 35983 [syscall]: runtime.cgocall(0x5900642c14a0, 0xc002411958) /usr/lib/golang/src/runtime/cgocall.go:157 +0x4b fp=0xc002411930 sp=0xc0024118f8 pc=0x590063012d6b github.com/containers/podman/vendor/github.com/containers/storage/pkg/idtools._Cfunc_subid_get_uid_ranges(0x79fd08039780, 0xc001e80048) _cgo_gotypes.go:123 +0x4f fp=0xc002411958 sp=0xc002411930 pc=0x5900633f7fcf github.com/containers/podman/vendor/github.com/containers/storage/pkg/idtools.readSubid.func3(0xc000b67c50?, 0x4?) /builddir/build/BUILD/containers-podman-1a6dca2/_build/src/github.com/containers/podman/vendor/github.com/containers/storage/pkg/idtools/idtools_supported.go:55 +0x4a fp=0xc002411998 sp=0xc002411958 pc=0x5900633f880a github.com/containers/podman/vendor/github.com/containers/storage/pkg/idtools.readSubid({0xc000b67c24, 0x7},...

Cache support for Nexus

1

## Is your feature/enhancement proposal related to a problem? Please describe. The http caching mechanism uses the sha sum as far as I can tell, when pointed to pypi.org requests's...