Refactor variables in plugin.sh to simplify setting a datastore
Refactor variables in plugin.sh to simplify setting a datastore

Remove several variables local to plugin.sh so it is possible to
set a non default datastore by changing only the 3 most obvious ones:

TROVE_DATASTORE_TYPE
TROVE_DATASTORE_VERSION
TROVE_DATASTORE_PACKAGE

Change-Id: I782757647985bdfb859043fe68e2b4cd27569ab3

openstack/trove,openstack/trove