core: improve logs in VdsManager

Fix mispellings, remove "resource manager" from logging statements
since it's a wrong class name, rephrase log statements to be more clear, remove
isDebugEnabled around logException (which is logged as error)

Change-Id: I815f0c7bdadc25be5fa3f0829114f1d7f2a2dddd
Signed-off-by: Alissa Bonas <abonas@redhat.com>