Update umoci - minimize xattr warnings

[dtrudg]

Description of the Pull Request (PR):

This updates our version of umoci to v0.4.2+singularity2 from the sylabs
fork.

This version contains a patch to only show a warning for the first
ENOTSUP error when handling xattrs on a filesystem that does not support
them (e.g. NFS mount). This prevents other warnings/errors being
obscured by huge numbers of unimportant ENOTSUP warnings.

Before:

singularity build -s mysandbox docker://centos:7
                      
INFO:    Starting build...
Getting image source signatures
Copying blob d8d02d457314 skipped: already exists
Copying config acab94af64 done
Writing manifest to image destination
Storing signatures
2019/10/23 12:20:43  info unpack layer: sha256:d8d02d45731499028db01b6fa35475f91d230628b4e25fab8e3c015594dc3261
2019/10/23 12:20:49  warn xattr{run/lock/lockdev} ignoring ENOTSUP on setxattr "user.rootlesscontainers"
2019/10/23 12:20:49  warn xattr{run/systemd/netif} ignoring ENOTSUP on setxattr "user.rootlesscontainers"
2019/10/23 12:20:49  warn xattr{run/systemd/netif/leases} ignoring ENOTSUP on setxattr "user.rootlesscontainers"
2019/10/23 12:20:49  warn xattr{run/systemd/netif/links} ignoring ENOTSUP on setxattr "user.rootlesscontainers"
2019/10/23 12:20:50  warn xattr{run/utmp} ignoring ENOTSUP on setxattr "user.rootlesscontainers"
2019/10/23 12:20:57  warn rootless{usr/bin/ping} ignoring (usually) harmless EPERM on setxattr "security.capability"
2019/10/23 12:21:02  warn xattr{usr/bin/write} ignoring ENOTSUP on setxattr "user.rootlesscontainers"
...
more warnings...

After (with this PR):

INFO:    Starting build...
Getting image source signatures
Copying blob d8d02d457314 skipped: already exists
Copying config acab94af64 done
Writing manifest to image destination
Storing signatures
2019/10/23 12:13:42  info unpack layer: sha256:d8d02d45731499028db01b6fa35475f91d230628b4e25fab8e3c015594dc3261
2019/10/23 12:13:47  warn xattr{run/lock/lockdev} ignoring ENOTSUP on setxattr "user.rootlesscontainers"
2019/10/23 12:13:47  warn xattr{rootfs-73ff226d-f5b8-11e9-b105-e0d55e6c2d0d/run/lock/lockdev} destination filesystem does not support xattrs, further warnings will be suppressed
2019/10/23 12:13:55  warn rootless{usr/bin/ping} ignoring (usually) harmless EPERM on setxattr "security.capability"
2019/10/23 12:15:18  warn rootless{usr/sbin/arping} ignoring (usually) harmless EPERM on setxattr "security.capability"
2019/10/23 12:15:18  warn rootless{usr/sbin/clockdiff} ignoring (usually) harmless EPERM on setxattr "security.capability"
INFO:    Creating sandbox directory...
INFO:    Build complete: mysandbox

This fixes or addresses the following GitHub issues:

• Fixes Minimize xattr warnings from umoci #4662

Before submitting a PR, make sure you have done the following:

• Read the Guidelines for Contributing, and this PR conforms to the stated requirements.
• Added changes to the CHANGELOG if necessary according to the Contribution Guidelines
• Added tests to validate this PR and tested this PR locally with a make testall
• Based this PR against the appropriate branch according to the Contribution Guidelines
• Added myself as a contributor to the Contributors File

Attn: @singularity-maintainers

[DrDaveD]

Looks good Dave, but what about the first warning that prompted us to fix the --silent option

warn rootless{usr/bin/ping} ignoring (usually) harmless EPERM on setxattr "security.capability"

which @afortiorama first reported in 4517?

[dtrudg]

@DrDaveD - Those are warnings that we are discarding something that may be there for a functional reason in the docker layer (ping does need a capability set to work). Having gone through some of the umoci stuff I'm not comfortable upstreaming something that would silence or downgrade them. They are warning of things that may actually create a rootfs in which things don't work as expected when you consider umoci being used other than for Singularity.

We are trying to move toward closer compliance with the original content of OCI layers, and e.g. Singularity is now usable as a CRI with k8s which inspires a need to think about more faithful compliance - so I don't really want to get rid of them.

On #4517 the log spam is mainly from selinux attrs which generally should be excluded from container images (I noted before that koji builds for some time should exclude them), and the -s is functional now.