Add alter to support cv_ttype_add(), cv_ttype_drop()

 - Add dbi routines alter, describe
 - Tests for alter

Change-Id: Ic0d624b02286b25c51cad5b5368613bc96c33824
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Finish support for tape types

 - Add cvv_ttype_populate()
 - In db.alter, bail if database is closed

Change-Id: Ib9bc8bd891d5286a50264d01265837303804fc1b
dbtype = {"hpss"|"crawler"}

 - Reworked DBI constructor so dbtype values are "hpss" and "crawler" and db2
   database names are in the config.

Change-Id: Ifb180475183e236f13158d4cc1d6add7ba8fc504