Instead of hard coding 10 hours as the default ticket lifetime within
lib/krb5/init_cred_pw.c init_cred(), add a preprocessor macro,
KRB5_TKT_LIFETIME_DEFAULT, that can be overridden at build time.
The value of KRB5_TKT_LIFETIME_DEFAULT is 10 hours if not previously
defined.
Change-Id: I63e729fedee8e8c6f542e4a4665de5f40db34c03