Fix: qcd may migrate host databases when is not needed.

The idea of using a glob to get a set of valid (existent) qcd databases, was
not working correctly because qcd was matching the files with a rather
permissive regular expression.

The problem manifested itself, when being in machine B, with a shared $HOME for
two machines A and B, and a .qcddb.A database in this $HOME. In this case, if I
executed qcd, the script would rename .qcddb.A into .qcddb.B, which was an
incorrect behavior.
Add back flexibility when choosing the database name

qcd allows the user to define the file name of the database for qcd. When I
introduced the support for multiple machines with the same host, I forgot about
it, and forced it to be "\.qcddb.*". I have change the pattern now, so that it
becomes as flexible as before.