Allow for specifying nfs mount options

Fixes bug 1113042

Adds a new config option:
    nfs_mount_options=None (Default)

When not None, anything set here will be passed as -o <options> to
the mount command. The default behavior is to do exactly as we are
doing today and relying on the OS/kernel defaults.

Change-Id: I935ae6f4d96c20904b7132fe8c6dfd3cbe089e51
Flags: DocImpact
Fix import for install_venv.py

On systems that don't use devstack the nova directory
doesn't automatically get added to the python path. This
breaks tools/install_venv_common.py which imports from
nova.openstack.common. This fixes the issue by manually
adding the nova root directory to the python path before
tools/install_venv_common.py is imported.

Change-Id: I8a3df02a51c2c777d8f47cb8bc72d0644ae47095
Make get_dev_name_for_instance() use stashed instance_type info

Related to blueprint no-db-compute

Change-Id: I6a8e357b69e6cfbdfa5be846b74baf6df3b8eae4
Merge "Allow for specifying nfs mount options"
Merge "Fix import for install_venv.py"