docker.client.APIError has moved to docker.errors.APIError

see https://github.com/dotcloud/docker-py/commit/18d4db09ecc79cef49830fa2c28c5e99dd02be42
Merge pull request #7029 from mattjbray/docker-api-error

docker.client.APIError has moved to docker.errors.APIError
hint to install python-ssl on redhat systems
Merge pull request #7044 from 42wim/devel

hint to install python-ssl on redhat systems
Determine selinux context for NFS mount points correctly

Fixes #7009
Make sure umask is set restrictively before creating any vault files
Updating changelog/releases/packaging for 1.5.5 release
Make sure HostVars object is instantiated before assigning it

Fixes #7006
Fix date in changelog for RPM builds off devel branch.
Merge branch 'issue_7009_nfs_selinux' into devel