Merge pull request moby#1178 from tonistiigi/1903-picks

[docker-19.03] docker 19.03 / v0.6.2 cherry picks

Merge pull request moby#1133 from tonistiigi/concurrent-write

remotecache: fix concurrent write

Merge pull request moby#1132 from tonistiigi/keep-git

git: updates for keep git dir

Merge pull request moby#1132 from tonistiigi/keep-git

git: updates for keep git dir

Merge pull request moby#1101 from tonistiigi/target-exists

exporter: allow oci exporters visibility to response metadata

Merge pull request moby#1101 from tonistiigi/target-exists

exporter: allow oci exporters visibility to response metadata

Merge pull request moby#1101 from tonistiigi/target-exists

exporter: allow oci exporters visibility to response metadata

Merge pull request moby#984 from AkihiroSuda/sd-notify

buildkitd: support sd_notify

Merge pull request moby#966 from tonistiigi/csv-fix

hack: fix csv values

Merge pull request moby#968 from tonistiigi/security-cap-fix

llb: fix security mode cap check