ExecOp: update content-cache mount logic #2318

Job	Run time
prepare	1s
test / prepare	1m 49s
test / run (containerd, ./frontend/dockerfile, integration)	4m 54s
test / run (containerd, ./frontend/dockerfile, dockerfile)	6m 39s
test / run (containerd-rootless, ./frontend/dockerfile, integration)	4m 39s
test / run (containerd-rootless, ./frontend/dockerfile, dockerfile)	5m 38s
test / run (containerd-1.6, ./frontend/dockerfile, integration)	5m 21s
test / run (containerd-1.6, ./frontend/dockerfile, dockerfile)	5m 47s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, integration)	5m 36s
test / run (containerd-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	7m 40s
test / run (oci, ./frontend/dockerfile, integration)	4m 5s
test / run (oci, ./frontend/dockerfile, dockerfile)	5m 12s
test / run (oci-rootless, ./frontend/dockerfile, integration)	4m 5s
test / run (oci-rootless, ./frontend/dockerfile, dockerfile)	5m 29s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, integration)	4m 11s
test / run (oci-rootless-slirp4netns-detachnetns, ./frontend/dockerfile, dockerfile)	5m 11s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, integration)	5m 5s
test / run (oci-snapshotter-stargz, ./frontend/dockerfile, dockerfile)	5m 14s
image (mainline)	5m 1s
image (labs)	4m 50s
release	0s
	1h 36m 27s

Provide feedback