earlephilhower Fix minor BearSSL API issues (#4901)
Fixes #4882 and updates GitHub certificate fingerprint to the current one
in BearSSL_Validation example.

When setting a authentication mode or stopping, clear all others out in case
the object is being re-used.

Add in a yield during the SSL handshake to allow a graceful timeout and not
a WDT error when the remote server hiccups.  Thanks to @Jeroen88 for
finding and testing this.
Latest commit 5309188 Jul 16, 2018