Translate internal errors into DBus-API-specific error values
Translate internal errors into DBus-API-specific error values

A StratisError can be of many different varieties, but we want to map all
of these to our fewer choices for DBus API error values.
internal_to_dbus_error() does this in a relatively coarse way that we can
improve on in the future.

Also, use this new function in create_pool().

Signed-off-by: Andy Grover <b7d524d2f5cc5aebadb6b92b08d3ab26911cde33@redhat.com>

trgill/stratisd,stratis-storage/stratisd,stratis-storage/stratisd,mulkieran/stratisd,stratis-storage/stratisd,trgill/stratisd,mulkieran/stratisd