powervm: Implement snapshot for local volumes

Snapshot local volumes by copying the logical volume on VIOS,
gzip the file, transfer to compute service node, and
finally upload to glance. PEP8 and string concatenation fixes.
Added utility to powervm.common for constructing UNIX file paths.
Added unit tests for new utility.

bp powervm-compute-enhancements

Change-Id: Ie6bafbeef75a9464457d78d2997be78346d3ab24
CLI for bare-metal database sync.

Part 3 of 6: blueprint general-bare-metal-provisioning-framework.

Change-Id: Ia19ce00edb84aa924c2ab2c9c2217f6b49073d69
Co-authored-by: Mikyung Kang <mkkang@isi.edu>
Co-authored-by: David Kang <dkang@isi.edu>
Co-authored-by: Ken Igarashi <igarashik@nttdocomo.co.jp>
Co-authored-by: Arata Notsu <notsu@virtualtech.jp>
Merge "powervm: Implement snapshot for local volumes"
Merge "CLI for bare-metal database sync."