Fix empty dir handling in phaino
Fix empty dir handling in phaino

If there's an emptyDir present in the volumes section, the function
resolveVolumeMounts puts an empty string in the map. This restores
the handling of that case. Otherwise errors occur like these:

docker: Error response from daemon: failed to create shim: OCI runtime
create failed: invalid mount {Destination::/mount-name Type:bind
Source:/var/lib/docker/volumes/a187...adfe/_data Options:[rbind]}:
mount destination :/mount-name not absolute: unknown.

Can also be seen when phaino is run in the log:

...
"-v" \
 ":/mount-name" \
...

Signed-off-by: Daniel Hiller <7d48ffa1ba2c479d4ee671710c0799f4b0a3eb8f@redhat.com>

kubernetes/test-infra,dims/test-infra,cjwagner/test-infra,dims/test-infra,kubernetes/test-infra,michelle192837/test-infra,cjwagner/test-infra,jessfraz/test-infra,jessfraz/test-infra,BenTheElder/test-infra,cjwagner/test-infra,fejta/test-infra,dims/test-infra,jessfraz/test-infra,kubernetes/test-infra,dims/test-infra,BenTheElder/test-infra,monopole/test-infra,cblecker/test-infra,kubernetes/test-infra,michelle192837/test-infra,jessfraz/test-infra,cjwagner/test-infra,fejta/test-infra,kubernetes/test-infra,cblecker/test-infra,dims/test-infra,jessfraz/test-infra,fejta/test-infra,michelle192837/test-infra,BenTheElder/test-infra,kubernetes/test-infra,cblecker/test-infra,monopole/test-infra,dims/test-infra,fejta/test-infra,fejta/test-infra,monopole/test-infra,jessfraz/test-infra,michelle192837/test-infra,cblecker/test-infra,cjwagner/test-infra,monopole/test-infra,BenTheElder/test-infra,monopole/test-infra,BenTheElder/test-infra,cjwagner/test-infra,cblecker/test-infra,michelle192837/test-infra,fejta/test-infra,monopole/test-infra,BenTheElder/test-infra,cblecker/test-infra,michelle192837/test-infra