As of w_2018_38 (and maybe a few versions earlier?), the butler ignores HDU specifications such as filename[0].  This breaks the code to handle auxTel data as we need to read raw_hdu from the PDU.

The problem seems to be that readMetadata has two ways that seem to specify an HDU, the cfitsio style filename[N] and an explicit hdu=N; in reality the second overrides the first.  It is not possible to support the cfitsio style syntax in afw without changing the default value for hdu as currently the default value means, "read the first data HDU" so it is not possible for the C++ to know whether to obey the [HDU] or the hdu. It would be possible for the C++ to reject the former, but it currently silently ignores it.

In consequence, the butler must parse the template and pass a bare filename and an HDU; this ticket requests that this be done.