stir_shaken: Fix propagation of attest_level and a few other values

stir_shaken: Fix propagation of attest_level and a few other values

attest_level, send_mky and check_tn_cert_public_url weren't
propagating correctly from the attestation object to the profile
and tn.

* In the case of attest_level, the enum needed to be changed
so the "0" value (the default) was "NOT_SET" instead of "A".  This
now allows the merging of the attestation object, profile and tn
to detect when a value isn't set and use the higher level value.

* For send_mky and check_tn_cert_public_url, the tn default was
forced to "NO" which always overrode the profile and attestation
objects.  Their defaults are now "NOT_SET" so the propagation
happens correctly.

* Just to remove some redundant code in tn_config.c, a bunch of calls to
generate_sorcery_enum_from_str() and generate_sorcery_enum_to_str() were
replaced with a single call to generate_acfg_common_sorcery_handlers().

Resolves: #904