[multi-sources-removal] Simplify ConnectionsSet internal structures and public methods
since it now handles a connection to the system source only
Related to #2919300
[jcr: adjust 3.17.11 migration, fix a number of bugs in new
ConnectionsSet implementation, fix
source.{open,close}_source_connections]
from yams import schema2sql as y2sql
dbhelper = repo.system_source.dbhelper
rdefdef = schema['CWSource'].rdef('name')
attrtype = y2sql.type_from_constraints(dbhelper, rdefdef.object, rdefdef.constraints).split()[0]
cursor = session.cnxset.cu
sql('UPDATE entities SET asource = source WHERE asource is NULL')
dbhelper.change_col_type(cursor, 'entities', 'asource', attrtype, False)
dbhelper.change_col_type(cursor, 'entities', 'source', attrtype, False)