Github bug #327: NFS pool workaround: i18n changes

Adding the warning/status messages used by the workaround

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Github bug #327: NFS pool workaround: timeout adjustments

Adding a smaller timeout in the 'prepare()' method of
libvirtstoragepool ('mount' and 'umount' commands).

Fixing an error in utils/run_command() that prevented the
TimeoutExpired exception to be raised sometimes.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>
Github bug #327: NFS pool workaround: model changes

Implementing a workaround in '_get_storagepool_vols_num',
'lookup', 'activate' and 'deactivate' methods to avoid
libvirt calls in NFS pools when the corresponding NFS server
is unreachable.

In the 'lookup' method the state of the pool returned in
such scenario is 'inaccessible' to warn the UI that the pool
isn't available for normal operation.

Signed-off-by: Daniel Henrique Barboza <danielhb@linux.vnet.ibm.com>