Update sample configs to include master_kdc

Where we have ATHENA.MIT.EDU stanzas in sample or test krb5.conf files
which define kdc entries, also define a master_kdc entry.  Remove
default_domain and v4_instance_convert entries in examples as they are
only needed for krb5/krb4 principal conversions.  In the krb5_conf.rst
example, remove enctype specifications as we don't want to encourage
their use when they aren't necessary, and remove a redundant
domain_realm entry.

ticket: 7901 (new)
In PKINIT, use library initializer for OpenSSL

Use a library initializer to prevent multiple threads using PKINIT
from concurently initializing OpenSSL functions.  For cases where
MT-safety is not assured by registering OpenSSL locking callbacks,
this significantly lowers the odds of crashes caused by races in
OpenSSL initialization.  (If OpenSSL initialization functions are
called by some other thread directly, crashes are still possible.)

[ghudson@mit.edu: simplify code changes and commit message]

ticket: 6413
Check for asprintf failure in kdb5_util create

In add_admin_princ, remove build_name_with_realm and call asprintf
directly instead.  Check for asprintf failure to avoid passing an
undefined pointer to krb5_parse_name.

[ghudson@mit.edu: rewrite commit message]

ticket: 7902 (new)
target_version: 1.12.2
tags: pullup