Import new additions to oslo's processutils.

trycmd() and ssh_execute() have been moved into oslo. Copy the
oslo version here. Conversion will occur in a later review.

Change-Id: I69926af33ff824f712ae2b8e4023233afe1dff2f
Convert to using newly imported processutils.

This change moves nova over to using the newly imported trycmd() and
ssh_execute() implementations from oslo's processutils.

Change-Id: Ied2bb1eeb0cbdc6903a4028a60c89ca9e23656b4
Remove duplicate gettext.install() calls

When commit 799a925 moved us to console scripts entry points, we moved
the gettext.install() call into nova/cmd/__init__.py but forgot to
remove it from some of the commands.

Since that move, we've switched to using gettextutils.install() which
supports a $NOVA_LOCALEDIR environment variable ... so calling install()
from these commands will actually break that support.

Change-Id: I1f959704551b35e95c5470a7aef900312db2e223
Show the cause of virt driver error

Make sure that the virt driver loading errors are shown with the
stacktrace attached. Otherwise the source of an import error can be
completely hidden. This is important here, since virt driver can fail
due to various issues, like quantum vif problem.

Change-Id: Icb90d348e4a4ddef5768ca32836bd95d94981499
Merge "Remove duplicate gettext.install() calls"
Merge "Import new additions to oslo's processutils."
Merge "Convert to using newly imported processutils."
Merge "Show the cause of virt driver error"