libvirt/guest.py: Update docstrings of block device methods
libvirt/guest.py: Update docstrings of block device methods

Spell out description of some parameters in the below methods:

  - abort_job(), a wrapper around libvirt blockJobAbort()
  - rebase(), a wrapper around libvirt blockRebase()
  - commit(), a wrapper around libvirt blockCommit()

And a minor edit to resize(), a wrapper around libvirt blockResize()

Change-Id: I1740bd88ccb56999b9d7041999d80828466a0193

rahulunair/nova,vmturbo/nova,jianghuaw/nova,vmturbo/nova,vmturbo/nova,mikalstill/nova,rajalokan/nova,Juniper/nova,Juniper/nova,rajalokan/nova,klmitch/nova,rahulunair/nova,vmturbo/nova,phenoxim/nova,openstack/nova,rajalokan/nova,rahulunair/nova,klmitch/nova,jianghuaw/nova,mahak/nova,hanlind/nova,mikalstill/nova,gooddata/openstack-nova,hanlind/nova,Juniper/nova,Juniper/nova,openstack/nova,hanlind/nova,mikalstill/nova,klmitch/nova,gooddata/openstack-nova,jianghuaw/nova,rajalokan/nova,gooddata/openstack-nova,mahak/nova,klmitch/nova,jianghuaw/nova,gooddata/openstack-nova,mahak/nova,openstack/nova,phenoxim/nova