Move table alters from cv_lib to dbschem

 - Add dbschem.alter_table()
 - In cv.py, do all table alters through dbschem.alter_table()
 - In cv_lib.py, remove dbalter()
 - Use py.test in Makefile rather than nosetests

Change-Id: I0196839bd3f65df20f3efaadb0ff13829a759b79
Consolidate table creates

 - ensure table creates go through dbschem.make_table()
 - dbschem.make_table() now returns info so the caller can tell whether the
   table was created or not
 - tweaks to Makefile, cronjob to make them better

Change-Id: I64ca56d568e962d21f7776e43d98ef6b49239b22
drop_table, closed, ctor_dbtype tests

 - Moved drop_table from crawl_lib to dbschem
 - Updated calls to use the one in dbschem
 - Track database closed status in DBI and decline operations on closed
   databases there
 - Adding ctor_dbtype tests

Change-Id: I0d1d8b9e136c58e68452b00070e063e21ba47b51